Axially compressible artificial intervertebral disc having limited rotation using a captured ball and socket joint with a solid ball and retaining cap

ABSTRACT

An artificial disc having a pair of opposing baseplates, for seating against opposing vertebral bone surfaces, separated by a ball and socket joint that includes a solid ball mounted to protrude from one of the baseplates. The ball is captured within a curvate socket formed in a peak of a convex structure integral with the other of the baseplates. The socket is formed by opposing curvate pockets, one on the convex structure and one on a retaining cap that is secured to the other of the baseplates. The ball rotates and angulates in the socket. The ball and socket joint therefore permits the baseplates to rotate and angulate relative to one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.patent application Ser. No. 10/256,160 (filed Sep. 26, 2002) now U.S.Pat. No. 6,989,032 entitled “Artificial Intervertebral Disc HavingLimited Rotation Using a Captured Ball and Socket Joint With a SolidBall and Compression Locking Post”, which is a continuation-in-partapplication of U.S. patent application Ser. No. 10/175,417 (filed Jun.19, 2002) entitled “Artificial Intervertebral Disc Utilizing a BallJoint Coupling”, which is a continuation-in-part application of U.S.patent application Ser. No. 10/151,280 (filed May 20, 2002) entitled“Tension Bearing Artificial Disc Providing a Centroid of MotionCentrally Located Within an Intervertebral Space”, which is acontinuation-in-part application of both U.S. patent application Ser.No. 09/970,479 (filed Oct. 4, 2001) now U.S. Pat. No. 6,669,730 entitled“Intervertebral Spacer Device Utilizing a Spirally Slotted BellevilleWasher Having Radially Extending Grooves” as well as U.S. patentapplication Ser. No. 10/140,153 (filed May 7, 2002) entitled “ArtificialIntervertebral Disc Having a Flexible Wire Mesh Vertebral Body ContactElement”, the former being a continuation-in-part application of U.S.patent application Ser. No. 09/968,046 (filed Oct. 1, 2001) nowabandoned entitled “Intervertebral Spacer Device Utilizing a BellevilleWasher Having Radially Extending Grooves” and the latter being acontinuation-in-part application of both U.S. patent application Ser.No. 09/970,479 now U.S. Pat. No. 6,669,730 (detailed above) as well asU.S. patent application Ser. No. 10/128,619 (filed Apr. 23, 2002) nowU.S. Pat. No. 6,863,689 entitled “Intervertebral Spacer Having aFlexible Wire Mesh Vertebral Body Contact Element”, which is acontinuation-in-part application of both U.S. patent application Ser.No. 09/906,119 (filed Jul. 16, 2001) now U.S. Pat. No. 6,607,559 andentitled “Trial Intervertebral Distraction Spacers” as well as U.S.patent application Ser. No. 09/982,148 (filed Oct. 18, 2001) now U.S.Pat. No. 6,673,113 and entitled “Intervertebral Spacer Device HavingArch Shaped Spring Elements”. All of the above mentioned applicationsare hereby incorporated by reference herein in their respectiveentireties.

FIELD OF THE INVENTION

This invention relates generally to a spinal implant assembly forimplantation into the intervertebral space between adjacent vertebralbones to simultaneously provide stabilization and continued flexibilityand proper anatomical motion, and more specifically to such a devicethat is axially compressible and has a captured ball and socket jointwith a solid ball and retaining cap.

BACKGROUND OF THE INVENTION

The bones and connective tissue of an adult human spinal column consistsof more than twenty discrete bones coupled sequentially to one anotherby a tri-joint complex that consists of an anterior disc and the twoposterior facet joints, the anterior discs of adjacent bones beingcushioned by cartilage spacers referred to as intervertebral discs.These more than twenty bones are anatomically categorized as beingmembers of one of four classifications: cervical, thoracic, lumbar, orsacral. The cervical portion of the spine, which comprises the top ofthe spine, up to the base of the skull, includes the first sevenvertebrae. The intermediate twelve bones are the thoracic vertebrae, andconnect to the lower spine comprising the five lumbar vertebrae. Thebase of the spine is the sacral bones (including the coccyx). Thecomponent bones of the cervical spine are generally smaller than thoseof the thoracic spine, which are in turn smaller than those of thelumbar region. The sacral region connects laterally to the pelvis. Whilethe sacral region is an integral part of the spine, for the purposes offusion surgeries and for this disclosure, the word spine shall referonly to the cervical, thoracic, and lumbar regions.

The spinal column is highly complex in that it includes these more thantwenty bones coupled to one another, housing and protecting criticalelements of the nervous system having innumerable peripheral nerves andcirculatory bodies in close proximity. In spite of these complications,the spine is a highly flexible structure, capable of a high degree ofcurvature and twist in nearly every direction.

Genetic or developmental irregularities, trauma, chronic stress, tumors,and degenerative wear are a few of the causes that can result in spinalpathologies for which surgical intervention may be necessary. A varietyof systems have been disclosed in the art that achieve immobilizationand/or fusion of adjacent bones by implanting artificial assemblies inor on the spinal column. The region of the back that needs to beimmobilized, as well as the individual variations in anatomy, determinethe appropriate surgical protocol and implantation assembly. Withrespect to the failure of the intervertebral disc, the interbody fusioncage has generated substantial interest because it can be implantedlaparoscopically into the anterior of the spine, thus reducing operatingroom time, patient recovery time, and scarification.

Referring now to FIGS. 13–14, in which a side perspective view of anintervertebral body cage and an anterior perspective view of a postimplantation spinal column are shown, respectively, a more completedescription of these devices of the prior art is herein provided. Thesecages 1 generally comprise tubular metal body 2 having an externalsurface threading 3. They are inserted transverse to the axis of thespine 4, into preformed cylindrical holes at the junction of adjacentvertebral bodies (in FIG. 14 the pair of cages 1 are inserted betweenthe fifth lumbar vertebra (L5) and the top of the sacrum (S1)). Twocages 1 are generally inserted side by side with the external threading4 tapping into the lower surface of the vertebral bone above (L5), andthe upper surface of the vertebral bone (S1) below. The cages 1 includeholes 5 through which the adjacent bones are to grow. Additionalmaterials, for example autogenous bone graft materials, may be insertedinto the hollow interior 6 of the cage 1 to incite or accelerate thegrowth of the bone into the cage. End caps (not shown) are oftenutilized to hold the bone graft material within the cage 1.

These cages of the prior art have enjoyed medical success in promotingfusion and grossly approximating proper disc height. It is, however,important to note that the fusion of the adjacent bones is an incompletesolution to the underlying pathology as it does not cure the ailment,but rather simply masks the pathology under a stabilizing bridge ofbone. This bone fusion limits the overall flexibility of the spinalcolumn and artificially constrains the normal motion of the patient.This constraint can cause collateral injury to the patient's spine asadditional stresses of motion, normally borne by the now-fused joint,are transferred onto the nearby facet joints and intervertebral discs.It would therefore, be a considerable advance in the art to provide animplant assembly which does not promote fusion, but, rather, whichmimics the biomechanical action of the natural disc cartilage, therebypermitting continued normal motion and stress distribution.

It is, therefore, an object of the invention to provide anintervertebral spacer that stabilizes the spine without promoting a bonefusion across the intervertebral space.

It is further an object of the invention to provide an implant devicethat stabilizes the spine while still permitting normal motion.

It is further an object of the invention to provide a device forimplantation into the intervertebral space that does not promote theabnormal distribution of biomechanical stresses on the patient's spine.

It is further an object of the invention to provide an artificial discthat provides free rotation of the baseplates relative to one another.

It is further an object of the invention to provide an artificial discthat provides limited rotation of the baseplates relative to oneanother.

It is further an object of the invention to provide an artificial discthat supports compression loads.

It is further an object of the invention to provide an artificial discthat permits the baseplates to axially compress toward one another undera compressive load.

It is further an object of the invention to provide an artificial discthat permits the baseplates to axially compress toward one another undera compressive load and restore to their original uncompressed relativepositions when the compressive load is relieved.

It is further an object of the invention to provide an artificial discthat supports tension loads.

It is further an object of the invention to provide an artificial discthat prevents lateral translation of the baseplates relative to oneanother.

It is further an object of the invention to provide an artificial discthat provides a centroid of motion centrally located within theintervertebral space.

It is further an object of the invention to provide an artificial discbaseplate attachment device (for attaching the baseplates of theartificial disc to the vertebral bones between which the disc isimplanted) with superior gripping and holding strength upon initialimplantation and thereafter.

It is further an object of the invention to provide an artificial discbaseplate attachment device that deflects during insertion of theartificial disc between vertebral bodies.

It is further an object of the invention to provide an artificial discbaseplate attachment device that conforms to the concave surface of avertebral body.

It is further an object of the invention to provide an artificial discbaseplate attachment device that does not restrict the angle at whichthe artificial disc can be implanted.

It is further an object of the invention to provide an implantattachment device (for attaching the implant to bone) with superiorgripping and holding strength upon initial implantation and thereafter.

It is further an object of the invention to provide an implantattachment device that is deflectable.

It is further an object of the invention to provide an implantattachment device that conforms to a concave bone surface.

Other objects of the invention not explicitly stated will be set forthand will be more clearly understood in conjunction with the descriptionsof the preferred embodiments disclosed hereafter.

SUMMARY OF THE INVENTION

The preceding objects are achieved by the invention, which is anartificial intervertebral disc or intervertebral spacer devicecomprising a pair of support members (e.g., spaced apart baseplates),each with an outwardly facing surface. Because the artificial disc is tobe positioned between the facing endplates of adjacent vertebral bodies,the baseplates are arranged in a substantially parallel planar alignment(or slightly offset relative to one another in accordance with properlordotic angulation) with the outwardly facing surfaces facing away fromone another. The baseplates are to mate with the vertebral bodies so asto not rotate relative thereto, but rather to permit the spinal segmentsto bend (and in some embodiments, axially compress) relative to oneanother in manners that mimic the natural motion of the spinal segment.This natural motion is permitted by the performance of a ball and socketjoint (and in some embodiments, a spring member) disposed between thesecured baseplates, and the securing of the baseplates to the vertebralbone is achieved through the use of a vertebral body contact elementattached to the outwardly facing surface of each baseplate.

Preferable vertebral body contact elements include, but are not limitedto, one or more of the following: a convex mesh, a convex solid dome,and one or more spikes. The convex mesh is preferably secured at itsperimeter to the outwardly facing surface of the respective baseplate.This can be accomplished in any effective manner, however, laser weldingand plasma coating burying are two preferred methods when the mesh iscomprised of metal. While domed in its initial undeflected conformation,the mesh deflects as necessary during insertion of the artificial discbetween vertebral bodies, and, once the artificial disc is seatedbetween the vertebral bodies, the mesh deforms as necessary underanatomical loads to reshape itself to the concave surface of thevertebral endplate. Thus, the mesh is deformably reshapeable underanatomical loads such that it conformably deflects against the concavesurface to securably engage the vertebral body endplate. Statedalternatively, because the mesh is convexly shaped and is secured at itsperimeter to the baseplate, the mesh is biased away from the baseplatebut moveable toward the plate (under a load overcoming the bias; such aload is present, for example, as an anatomical load in theintervertebral space) so that it will securably engage the vertebralbody endplate when disposed in the intervertebral space. This affordsthe baseplate having the mesh substantially superior gripping andholding strength upon initial implantation, as compared with otherartificial disc products. The convex mesh further provides anosteoconductive surface through which the bone may ultimately grow. Themesh preferably is comprised of titanium, but can also be formed fromother metals and/or non-metals. Inasmuch as the mesh is domed, it doesnot restrict the angle at which the artificial disc can be implanted. Itshould be understood that while the flexible dome is described hereinpreferably as a wire mesh, other meshed or solid flexible elements canalso be used, including flexible elements comprised of non-metals and/orother metals. Further, the flexibility, deflectability and/ordeformability need not be provided by a flexible material, but canadditionally or alternatively be provided mechanically or by othermeans.

It should be understood that the convex mesh attachment devices andmethods described herein can be used not only with the artificial discsand artificial disc baseplates described or referred to herein, but alsowith other artificial discs and artificial disc baseplates, including,but not limited to, those currently known in the art. Therefore, thedescription of the mesh attachment devices and methods being used withthe artificial discs and artificial disc baseplates described orreferred to herein should not be construed as limiting the applicationand/or usefulness of the mesh attachment device.

To enhance the securing of the baseplates to the vertebral bones, eachbaseplate further comprises a porous area, which at least extends in aring around the lateral rim of each outwardly facing surface. The porousarea may be, for example, a sprayed deposition layer, or an adhesiveapplied beaded metal layer, or another suitable porous coating known inthe art. The porous ring permits the long-term ingrowth of vertebralbone into the baseplate, thus permanently securing the prosthesis withinthe intervertebral space. The porous layer may extend beneath the domedmesh as well, but is more importantly applied to the lateral rim of theoutwardly facing surface of the baseplate that seats directly againstthe vertebral body.

Some of the embodiments described herein uses two baseplates each havingthe above described convex mesh on its outwardly facing surface, whileother embodiments use two baseplates each having a convex solid dome incombination with a plurality of spikes on the lateral rim of theoutwardly facing surface of the baseplates. It should be understood,however, that the various attachments devices or methods describedherein (as well as any other attachment devices or methods, such as, forexample, keels) can be used individually or in combination in anypermutation, without departing from the scope of the present invention.

The ball and socket joint disposed between the baseplates permitsrotation and angulation of the two baseplates relative to one anotherabout a centroid of motion centrally located between the baseplates. Awide variety of embodiments are contemplated, some in which the ball andsocket joint permits free relative rotation of the baseplates, andothers in which the ball and socket joint limits relative rotation ofthe baseplates to a certain range. Further in some embodiments, the balland socket joint is used in conjunction with a spring member toadditionally permit the two baseplates to axially compress relative toone another. Further in each of the embodiments, the assembly will notseparate under tension loading, and prevents lateral translation of thebaseplates during rotation and angulation.

More particularly, four embodiment families are described herein asexamples of the present invention, with a preferred embodiment for thefirst embodiment family, a preferred embodiment for the secondembodiment family, five preferred embodiments for the third embodimentfamily, and five embodiments for the fourth embodiment family, eachbeing described in detail. However, it should be understood that thedescribed embodiments and embodiment families are merely examples thatillustrate aspects and features of the present invention, and that otherembodiments and embodiment families are possible without departing fromthe scope of the invention.

Each of the embodiments in the four embodiment families discussed hereinshare the same basic elements, some of which retain identicalfunctionality and configuration across the embodiments, and some ofwhich gain or lose functionality and/or configuration across theembodiments to accommodate mechanical and/or manufacturing necessities.More specifically, each of the embodiments includes two baseplatesjoined to one another by a ball and socket joint that is establishedcentrally between the baseplates. Each ball and socket joint isestablished by a socket being formed at the peak (or in the peak) of aconvex structure extending from the second baseplate, and by a ballbeing secured to the first baseplate and being captured in the socket sothat when the joint is placed under a tension or compression force, theball remains rotatably and angulatably secure in the socket. However,the convex structure is configured differently in each of the embodimentfamilies, and the manner in which the ball is captured in the socket isdifferent in each of the embodiment families. Each of these twovariations (the configuration of the convex structure and the manner ofcapturing the ball in the socket) among the embodiments families issummarized immediately below, and will be understood further in light ofthe additional descriptions of the embodiments herein. It should benoted that although each of the embodiment families uses a preferredshape for the convex structure (e.g., in the first and second embodimentfamilies, the preferred shape is frusto-conical, and in the third andfourth embodiment families, the preferred shape is a shape having acurved taper), the convex structure in each of the embodiment familiesis not limited to a particular shape. For example, shapes including, butnot limited to, frusto-conical, hemispherical or semispherical shapes,shapes having sloped tapers or curved tapers, or shapes havingnon-uniform, irregular or dimensionally varying tapers or contours,would also be suitable in any of the embodiment families.

With regard to the first embodiment family, the convex structure isconfigured as a flexible element and functions as a spring element thatprovides axial cushioning to the device. The convex structure has thesocket of the ball and socket joint at its peak. In order to permit theflexible convex structure to flex under compressive loads applied to thedevice, it is separated from the second baseplate. In the preferredembodiment, the flexible convex structure is a belleville washer thathas a frusto-conical shape. Other flexible convex structures are alsocontemplated as being suitable, such as, for example, convex structuresthat flex because of the resilience of the material from which they aremade, because of the shape into which they are formed, and/or or becauseof the mechanical interaction between sub-elements of an assemblyforming the convex structure. Although the convex structure is aseparate element from the second baseplate in this embodiment family(because it must be allowed to flex), it is preferably maintained nearthe second baseplate so that the device does not separate in tension.Therefore, an extension of the second baseplate is provided (in the formof a shield element) to cover enough of the convex structure to somaintain it. Stated alternatively, the shield is a separate element fromthe second baseplate to ease manufacturing (during assembly, theflexible convex structure is first placed against the second baseplate,and then the shield is placed over the convex structure and secured tothe second baseplate so that the convex structure is maintained betweenthe second baseplate and the shield), but once the device is assembled,the second baseplate and the shield are effectively one element. Thatis, the second baseplate and shield can be considered to be a singleintegral housing within which the separate flexible convex structureflexes, because but for the sake of achieving desirable manufacturingefficiencies, the second baseplate and shield would be one piece.

Also with regard to the first embodiment family, the manner of capturingthe ball in the socket is effected by the ball being selectivelyradially compressible. That is, the ball is radially compressible to fitinto the socket and thereafter receives a deflection preventing elementto prevent subsequent radial compression, so that the ball remainscaptured in the socket. A more detailed description of the preferredmanner in which this is accomplished is described below. Because thesocket is formed at the peak of the flexible convex structure discussedimmediately above, the capturing of the ball in the socket in thismanner allows the ball to remain securely held for rotation andangulation even though the socket moves upward and downward with theflexing of the convex structure. The second baseplate preferablyincludes an access hole that facilitates the capture of the ball in thesocket; in this embodiment family, it facilitates the capture byaccommodating placement of the deflection preventing element, so thatthe same can be applied to the ball after the ball is fitted into thesocket. Accordingly, the ball is maintained in the socket.

With regard to the second embodiment family, the convex structure isconfigured as a non-flexible element that is integral with the secondbaseplate, and has the socket of the ball and socket joint at its peak.More clearly stated, the devices of this second embodiment family do notfeature a flexible convex structure, and therefore (and also because ofthe manner in which the ball is captured in this second embodimentfamily, discussed immediately below) there is no need for the convexstructure to be a separate element from the second baseplate. (Bycontrast, in the first embodiment family, as discussed above, becausethe convex structure is flexible, it is a separate element than thesecond baseplate so that it is able to flex.) In the preferredembodiment, the convex structure has a frusto-conical shape. The mannerof capturing the ball in the socket in this second embodiment family isidentical to that of the first embodiment family.

With regard to the third embodiment family, the convex structure isconfigured as a non-flexible element that is integral with the secondbaseplate, and has the socket of the ball and socket joint in its peak,similar to the configuration of the convex structure in the secondembodiment family. In the preferred embodiment, the convex structure isshaped to have a curved taper. The manner of capturing the ball in thesocket of this third embodiment family is effected through the use of asolid ball. In order to permit the seating of the ball into the socket,the second baseplate has an access hole that facilitates the capture ofthe ball in the socket; in this embodiment family, the access holefacilitates the capture in that it has a diameter that accommodates thediameter of the ball, and leads to the interior of the peak, whichinterior is formed as a concavity having an opening diameter thataccommodates the diameter of the ball. (Preferably, the concavity has acurvature closely accommodating the contour of the ball, and theconcavity is either hemispherical or less-than-hemispherical so that theball can easily be placed into it.) Further, in order to maintain theball in the socket, an extension of the second baseplate (in the form ofa cap element) is provided for sealing the access hole in the secondbaseplate (or reducing the opening diameter of the access hole to a sizethat does not accommodate the diameter of the ball). The cap has aninterior face that preferably has a concavity (that has a curvature thatclosely accommodates the contour of the ball) to complete the socket.The peak of the convex structure also has a bore that accommodates apost to which the ball and the first baseplate are attached (one to eachend of the post), but does not accommodate the ball for passage throughthe bore. Accordingly, the ball is maintained in the socket.

With regard to the fourth embodiment family, the convex structure isconfigured as a non-flexible element that is a separate element from,but attached to, the second baseplate, and has the socket of the balland socket joint in its peak. In the preferred embodiment, the convexstructure is shaped to have a curved taper, similar to the configurationof the convex structure in the third embodiment family. The convexstructure in this fourth embodiment family is separate from the secondbaseplate during assembly of the device, for reasons related to themanner in which the ball is captured in the socket, but is attached tothe second baseplate by the time assembly is complete. The manner ofcapturing the ball in the socket of this fourth embodiment family iseffected through the use of a solid ball. The ball is first seatedagainst the central portion of the second baseplate (which centralportion preferably has a concavity that has a curvature that closelyaccommodates the contour of the ball), and then the convex structure isplaced over the ball to seat the ball in the socket formed in theinterior of the peak of the convex structure (the interior is preferablyformed as a concavity that is either hemispherical orless-than-hemispherical so that the ball can easily fit into it). Afterthe convex structure is placed over the ball, the convex structure isattached to the second baseplate to secure the ball in the socket. As inthe third embodiment family, the peak of the convex structure also has abore that accommodates a post to which the ball and the first baseplateare attached (one to each end of the post), but does not accommodate theball for passage through the bore. Accordingly, the ball is maintainedin the socket.

It should be understood that each of the features of each of theembodiments described herein, including, but not limited to, formationsand functions of convex structures, manners of capturing the ball in thesocket, types of spring elements, and manners of limiting rotation ofthe baseplates relative to one another, can be included in otherembodiments, individually or with one or more others of the features, inother permutations of the features, including permutations that are notspecifically described herein, without departing from the scope of thepresent invention.

Each of the embodiment families will now be summarized in greaterdetail.

In the first embodiment family, the ball and socket joint includes aradially compressible ball (which, in some embodiments, is shaped as asemisphere), mounted to protrude from an inwardly facing surface of afirst baseplate, and a curvate socket formed at a peak of a flexibleconvex structure that is flexibly maintained near a second baseplate,within which curvate socket the ball is capturable for free rotation andangulation therein. Because the convex structure is flexible, itfunctions as a force restoring element (e.g., a spring) that providesaxial cushioning to the device, by deflecting under a compressive loadand restoring when the load is relieved. The flexible convex structureis preferably a belleville washer that has a frusto-conical shape. Ingeneral, a belleville washer is one of the strongest configurations fora spring, and is highly suitable for use as a restoring force providingelement in an artificial intervertebral disc which must endureconsiderable cyclical loading in an active human adult.

Belleville washers are washers that are generally bowed in the radialdirection (e.g., have a hemispherical or semispherical shape) or slopedin the radial direction (e.g., have a frusto-conical shape). Bowedbelleville washers have a radial convexity (i.e., the height of thewasher is not linearly related to the radial distance, but may, forexample, be parabolic in shape). In a sloped belleville washer, theheight of the washer is linearly related to the radial distance. Ofcourse, other shape variations of belleville washers are suitable (suchas, but not limited to, belleville washers having non-uniform tapers orirregular overall shapes). The restoring force of a belleville washer isproportional to the elastic properties of the material. In addition, themagnitude of the compressive load support and the restoring forceprovided by the belleville washer may be modified by providing slotsand/or grooves in the washer. The belleville washer utilized as theforce restoring member in the illustrated embodiment is spirallyslotted, with the slots initiating on the periphery of the washer andextending along arcs that are generally radially inwardly directed adistance toward the center of the bowed disc, and has radially extendinggrooves that decrease in width and depth from the outside edge of thewasher toward the center of the washer. As a compressive load is appliedto a belleville washer, the forces are directed into a hoop stress thattends to radially expand the washer. This hoop stress is counterbalancedby the material strength of the washer, and the strain of the materialcauses a deflection in the height of the washer. Stated equivalently, abelleville washer responds to a compressive load by deflectingcompressively, but provides a restoring force that is proportional tothe elastic modulus of the material in a hoop stressed condition. Withslots and/or grooves formed in the washer, it expands and restoresitself far more elastically than a solid washer.

In order to permit the flexible convex structure to flex undercompressive loads applied to the device, it is a separate element fromthe second baseplate in the preferred embodiment. To provide room forthe flexible convex structure to expand in unrestricted fashion when itis compressed, while generally maintaining the flexible convex structurewithin a central area near the second baseplate, the wide end of theflexible convex structure is housed in the second baseplate through theuse of an extension of the second baseplate structure (in the form of ashield element that is secured to the second baseplate). Moreparticularly, a circular recess is provided on an inwardly facingsurface of the second baseplate, and the wide end of the flexible convexstructure is seated into the recess. The extension of the secondbaseplate (e.g., a shield) is placed over the flexible convex structureto cover enough of the convex structure to prevent it from escaping therecess, and then is attached to the second baseplate. As stated above,the shield is a separate element from the second baseplate to easemanufacturing, but once the device is assembled, the second baseplateand the shield are effectively one element. That is, the secondbaseplate and shield can be considered to be a single integral housingwithin which the separate flexible convex structure flexes, because butfor the sake of achieving desirable manufacturing efficiencies, thesecond baseplate and shield would be one piece.

More particularly with regard to the ball, the ball includes a series ofslots that render it radially compressible and expandable incorrespondence with a radial pressure. The ball further includes anaxial bore that accepts a deflection preventing element (e.g., a rivet).Prior to the insertion of the rivet, the ball can deflect radiallyinward because the slots will narrow under a radial pressure. Theinsertion of the rivet eliminates the capacity for this deflection.Therefore, the ball, before receiving the rivet, can be compressed topass into, and thereafter seat in, the curvate socket of the secondbaseplate. (The curvate socket has an opening diameter that accommodatespassage therethrough of the ball in a radially compressed state (but notin an uncompressed state), and a larger inner diameter that accommodatesthe ball in the uncompressed state.) Once the ball has been seated inthe curvate socket, the rivet can be inserted into the axial bore toensure that the ball remains held in the curvate socket. The secondbaseplate preferably includes an access hole that accommodates placementof the deflection preventing element, so that the same can be applied tothe ball after the ball is fitted into the socket.

The curvate socket defines a spherical contour that closely accommodatesthe ball for free rotation and angulation in its uncompressed state.Therefore, when seated in the curvate socket, the ball can rotate andangulate freely relative to the curvate socket through a range ofangles, thus permitting the opposing baseplates to rotate and angulatefreely relative to one another through a corresponding range of anglesequivalent to the fraction of normal human spine rotation and angulation(to mimic normal disc rotation and angulation). The flexible convexstructure serving as a force restoring device further providesspring-like performance with respect to axial compressive loads, as wellas long cycle life to mimic the axial biomechanical performance of thenormal human intervertebral disc. Because the ball is held within thecurvate socket by a rivet in the axial bore preventing radialcompression of the protuberance, the artificial disc can withstandtension loading of the baseplates—the assembly does not come apart undernormally experienced tension loads. Thus, in combination with thesecuring of the baseplates to the adjacent vertebral bones via the meshdomes, the disc assembly has an integrity similar to the tension-bearingintegrity of a healthy natural intervertebral disc. Also because theball is laterally captured in the curvate socket, lateral translation ofthe baseplates relative to one another is prevented during rotation andangulation, similar to the performance of healthy natural intervertebraldisc. Because the baseplates are made angulatable relative to oneanother by the ball being rotatably and angulatably coupled in thecurvate socket, the disc assembly provides a centroid of motion withinthe sphere defined by the ball. Accordingly, the centroid of motion ofthe disc assembly remains centrally located between the vertebralbodies, similar to the centroid of motion in a healthy naturalintervertebral disc.

In the second embodiment family, the ball and socket joint includes aradially compressible ball (or in some embodiments, a semisphere)mounted to protrude from an inwardly facing surface of a firstbaseplate, and a curvate socket formed at a peak of a non-flexibleconvex structure that is integral with a second baseplate, within whichcurvate socket the ball is capturable for free rotation and angulationtherein. Because the convex structure is not flexible, it does not serveas a force restoring element (e.g., a spring). In the preferredembodiment, the convex structure has a frusto-conical shape. Theformation of the curvate socket, the configuration of the ball for usetherewith, and the manner in which the ball is captured in the socket,are preferably identical to that of the first embodiment family.Accordingly, the embodiments of the second embodiment family enjoy thecharacteristics and performance features of the embodiments of the firstembodiment family, except for the axial cushioning.

In the third embodiment family, the ball and socket joint includes asolid ball (which, in some embodiments, is shaped as a semisphere)mounted to protrude from an inwardly facing surface of a firstbaseplate, and a curvate socket formed in a peak of a non-flexibleconvex structure that is integral with a second baseplate, within whichcurvate socket the ball is capturable for free rotation and angulationtherein. In the preferred embodiment, the convex structure is shaped tohave a curved taper. With regard to the mounting of the ball, themounting includes a central post. A tail end of the post is (as a finalstep in the preferred assembly process) secured within a bore throughthe first baseplate, from the inwardly facing surface of the firstbaseplate to its outwardly facing surface. The ball is mounted at a headend of the post. The curvate socket defines a spherical contour, and isformed by opposing curvate pockets, one formed on a central portion ofan outwardly facing surface of the convex structure and one formed on aninwardly facing surface of an extension of the second baseplate (theextension being in the form of a cap element) that secures to theoutwardly facing surface of the second baseplate. When the cap issecured to the outwardly facing surface of the second baseplate, theopposing curvate pockets together form the curvate socket within whichthe ball freely rotates and angulates. Each curvate pocket issemispherically (preferably hemispherically) contoured to closelyaccommodate the spherical contour defined by the ball, so that the ballcan freely rotate in the socket about the longitudinal axis of the post,and can freely angulate in the socket about a centroid of motion locatedat the center of the sphere defined by the ball.

In order to enable the seating of the ball into the curvate socket, theaccess hole in the second baseplate leading to the outwardly facingsurface of the convex structure has a diameter that accommodates thediameter of the ball, and the curvate pocket on the outwardly facingsurface of the convex structure has an opening diameter thataccommodates the ball for seating in the pocket. Thus, the ball can beplaced through the access hole and into the curvate pocket. Thereafter,the cap is applied to seal the access hole in the second baseplate (orreduce the diameter of the access hole to a size that does notaccommodate the diameter of the ball). With regard to the attachment ofthe post to the first baseplate, the peak of the convex structure has acentral bore that accommodates the diameter of the post, but not thediameter of the ball. Therefore, as the ball is being placed into thecurvate pocket on the outwardly facing surface of the convex structure,the post fits through the bore, but the ball does not. After the cap issecured, the tail end of the post that is protruding from the bore issecured to the inwardly facing surface of the first baseplate by thetail end of the post preferably compression locking into a central borein the first baseplate.

In some embodiments of the third embodiment family, the cap elementincludes a spring member, preferably disposed on the curvate pocket orbetween the curvate pocket and the remaining structure of the capelement. The spring member can be attached to the curvate pocket and/orthe remaining structure of the cap element, or the spring member can bea separate element that is captured or maintained at least in partbetween the curvate pocket and the remaining structure of the capelement (in which embodiment the cap element may include multiplepieces). While not limited to any particular structure, assembly, ormaterial, a spring member providing shock absorption preferably includesan elastomeric material, such as, for example, polyurethane or silicon,and a spring member providing shock dampening preferably includes aplastic material, such as, for example, polyethylene. It should beunderstood that metal springs may alternatively or additionally be used.Accordingly, in such embodiments, part or all of a compressive loadapplied to the baseplates will be borne by the spring member, which willdampen the load and/or absorb the load and preferably help return thebaseplates to their original uncompressed relative positions.

Accordingly, the baseplates are rotatable relative to one anotherbecause the ball rotates freely within the socket, and angulatablerelative to one another because the ball angulates freely within thesocket. (In the embodiments further having the spring member, thebaseplates are also axially compressible relative to one another.)Because the ball is held within the socket by the securing of the tailend of the post to the first baseplate and the securing of the cap tothe second baseplate, the artificial disc can withstand tension loadingof the baseplates—the assembly does not come apart under normallyexperienced tension loads. Thus, in combination with the securing of thebaseplates to the adjacent vertebral bones, the disc assembly has anintegrity similar to the tension-bearing integrity of a healthy naturalintervertebral disc. Also because the ball is laterally captured in thesocket, lateral translation of the baseplates relative to one another isprevented during rotation and angulation, similar to the performance ofhealthy natural intervertebral disc. Because the baseplates are madeangulatable relative to one another by the ball being rotatably andangulatably coupled in the socket, the disc assembly provides a centroidof motion within the ball. Accordingly, the centroid of motion of thedisc assembly remains centrally located between the vertebral bodies,similar to the centroid of motion in a healthy natural intervertebraldisc.

Some embodiments in the third embodiment family limit the rotation (butpreferably not the angulation) of the ball in the socket. Eachembodiment accomplishes this in a different manner, but each embodimentutilizes interference between a protrusion and a recess to limit therotation. In some embodiments, the protrusion is preferablyhemispherical, and the recess preferably has a semicylindrical contourwithin which the protrusion fits. In other embodiments, the protrusionis preferably hemispherical, and the recess preferably has a curvatecontour that is not semicylindrical. (It should be understood that thedescribed formations of the recess and the protrusion are merelypreferred, and that alternate formations, curvate or otherwise, for eachare contemplated by the present invention; a particular shape orlocation of recess or a particular shape or location of protrusion isnot required; any shape can be used so long as the recess and protrusioninteract as desired.) The boundaries of the recess define the limits ofrotation of the ball within the socket, by allowing movement of theprotrusion relative to the recess as the ball rotates through a certainrange in the socket, but providing interference with the protrusion toprevent rotation of the ball beyond that range in the socket. At thesame time, the boundaries of the recess preferably do not limit theangulation of the ball within the socket, at least until the perimeterregions of the inwardly facing surfaces meet.

More particularly with respect to the manner in which these embodimentslimit rotation, in some embodiments the ball has a protrusion thatinterferes with a recess adjacent the socket, the recess being formed bya curvate recess adjacent the curvate pocket on the central portion ofthe outwardly facing surface of the convex structure and a curvaterecess adjacent the curvate pocket on the cap. In other embodiments, thehousing (e.g., the second baseplate/convex structure and/or the cap) hasa protrusion (e.g., a hemispherical protrusion or a hemispherical headof a pin secured in a pin hole in the housing) that interferes with arecess on the ball. In still other embodiments, each of the housing(e.g., the second baseplate/convex structure and/or the cap) and theball has a recess, and a ball bearing fits within the recesses, so thatthe ball bearing functions as a protrusion that interferes with one orboth of the recesses.

Therefore, when assembled, these embodiments of the third embodimentfamily enable angulation and limited rotation of the baseplates relativeto one another about a centroid of motion that remains centrally locatedbetween the baseplates (at the center of the sphere defined by theball), similar to the centroid of motion in a healthy naturalintervertebral disc that is limited in its rotation by surrounding bodystructures. A benefit of limiting the relative rotation of thebaseplates is that relative rotation beyond a certain range in a healthynatural disc is neither needed nor desired, because, for example, excessstrain can be placed on the facet joints or ligaments thereby. Asdescribed with the rotationally free embodiments of the secondembodiment family, the construction also prevents translation andseparation of the baseplates relative to one another during rotation andangulation.

In the fourth embodiment family, the ball and socket joint includes asolid ball (which, in some embodiments, is shaped as a semisphere)mounted to protrude from an inwardly facing surface of a firstbaseplate, and a curvate socket formed in a peak of a non-flexibleconvex structure that is attached to an inwardly facing surface of asecond baseplate, within which curvate socket the ball is capturable forfree rotation and angulation therein. In the preferred embodiment, theconvex structure is shaped to have a curved taper. With regard to themounting of the ball, the mounting includes a central post that extendsfrom the inwardly facing surface of the first baseplate. The ball is (asa final step in the preferred assembly process) mounted at a head end ofthe post, by the head end preferably compression locking into a centralbore in the ball. The curvate socket defines a spherical contour, and isformed by opposing curvate pockets, one formed on an inwardly facingsurface of the second baseplate, and one formed as a curvate tapered lipof a central bore that passes through a central portion of the convexstructure from the convex structure's outwardly facing surface (havingthe curvate tapered lip) to its inwardly facing surface. When the convexstructure is secured to the inwardly facing surface of the secondbaseplate, the opposing curvate pockets together form the curvate socketwithin which the ball freely rotates and angulates. Each curvate pocketis semispherically (preferably hemispherically) contoured to closelyaccommodate the spherical contour defined by the ball, so that the ballcan freely rotate in each pocket about the longitudinal axis of thepost, and can freely angulate in each pocket about a centroid of motionlocated at the center of the sphere defined by the ball.

In order to enable the seating of the ball into the curvate socket, thecurvate pocket on the inwardly facing surface of the second baseplatehas an opening diameter that accommodates the ball for seating in thepocket. Thus, the ball can be placed into the curvate pocket before theconvex structure is attached to the second baseplate. Thereafter, theconvex structure is attached to the inwardly facing surface of thesecond baseplate with the convex structure's curvate pocket (the curvatetapered lip of the convex structure's central bore) fitting against theball to complete the ball and socket joint. With regard to completingthe assembly, the central bore of the convex structure has a diameterthat accommodates the diameter of the post, but not the diameter of theball. Therefore, after the ball is secured in the curvate socket, thepost fits through the bore so that the head end of the post can becompression locked to the ball, but the ball is prevented from escapingthe socket through the central bore of the convex structure.

In some embodiments of the fourth embodiment family, the secondbaseplate includes a spring member, preferably disposed on the curvatepocket or between the curvate pocket and the remaining structure of thesecond baseplate. The spring member can be attached to the curvatepocket and/or the remaining structure of the second baseplate, or thespring member can be a separate element that is captured or maintainedat least in part between the curvate pocket and the remaining structureof the second baseplate (in which embodiment the second baseplate mayinclude multiple pieces). While not limited to any particular structure,assembly, or material, a spring member providing shock absorptionpreferably includes an elastomeric material, such as, for example,polyurethane or silicon, and a spring member providing shock dampeningpreferably includes a plastic material, such as, for example,polyethylene. It should be understood that metal springs mayalternatively or additionally be used. Accordingly, in such embodiments,part or all of a compressive load applied to the baseplates will beborne by the spring member, which will dampen the load and/or absorb theload and preferably help return the baseplates to their originaluncompressed relative positions.

Accordingly, the baseplates are rotatable relative to one anotherbecause the ball rotates freely within the socket, and angulatablerelative to one another because the ball angulates freely within thesocket. (In the embodiments further having the spring member, thebaseplates are also axially compressible relative to one another.)Because the ball is held within the socket by the securing of thecentral post of the first baseplate to the ball and the securing of theconvex structure to the second baseplate, the artificial disc canwithstand tension loading of the baseplates—the assembly does not comeapart under normally experienced tension loads. Thus, in combinationwith the securing of the baseplates to the adjacent vertebral bones, thedisc assembly has an integrity similar to the tension-bearing integrityof a healthy natural intervertebral disc. Also because the ball islaterally captured in the socket, lateral translation of the baseplatesrelative to one another is prevented during rotation and angulation,similar to the performance of healthy natural intervertebral disc.Because the baseplates are made angulatable relative to one another bythe ball being rotatably and angulatably coupled in the socket, the discassembly provides a centroid of motion within the sphere defined by theball. Accordingly, the centroid of motion of the disc assembly remainscentrally located between the vertebral bodies, similar to the centroidof motion in a healthy natural intervertebral disc.

Some embodiments in the fourth embodiment family limit the rotation (butpreferably not the angulation) of the ball in the socket formed by thecurvate taper of the convex structure and the hemispherical contour ofthe curvate pocket of the second baseplate. Each embodiment accomplishesthis in a different manner, but each embodiment utilizes interferencebetween a protrusion and a recess to limit the rotation, similar to themanner in which such interference is utilized in the third embodimentfamily. In some embodiments, the protrusion is preferably hemispherical,and the recess preferably has a semicylindrical contour within which theprotrusion fits. In other embodiments, the protrusion is preferablyhemispherical, and the recess preferably has a curvate contour that isnot semicylindrical. (It should be understood that the describedformations of the recess and the protrusion are merely preferred, andthat alternate formations, curvate or otherwise, for each arecontemplated by the present invention; a particular shape or location ofrecess or a particular shape or location of protrusion is not required;any shape can be used so long as the recess and protrusion interact asdesired.) The boundaries of the recess define the limits of rotation ofthe ball within the socket, by allowing movement of the protrusionrelative to the recess as the ball rotates through a certain range inthe socket, but providing interference with the protrusion to preventrotation of the ball beyond that range in the socket. At the same time,the boundaries of the recess preferably do not limit the angulation ofthe ball within the socket, at least until the perimeter regions of theinwardly facing surface of the convex structure and the inwardly facingsurface of the first baseplate meet.

More particularly with respect to the manner in which these embodimentslimit rotation, in some embodiments the ball has a protrusion thatinterferes with a recess adjacent the socket, the recess being formed bya curvate recess adjacent the curvate pocket on the second baseplate anda curvate recess adjacent the curvate taper on the convex structure. Inother embodiments, the housing (e.g., the second baseplate and/or theconvex structure) has a protrusion (e.g., a hemispherical protrusion ora hemispherical head of a pin secured in a pin hole in the housing) thatinterferes with a recess on the ball. In still other embodiments, eachof the housing (e.g., the second baseplate and/or the convex structure)and the ball has a recess, and a ball bearing fits within the recesses,so that the ball bearing functions as a protrusion that interferes withone or both of the recesses.

Therefore, when assembled, these embodiments of the fourth embodimentfamily enable angulation and limited rotation of the baseplates relativeto one another about a centroid of motion that remains centrally locatedbetween the baseplates (at the center of the sphere defined by theball), similar to the centroid of motion in a healthy naturalintervertebral disc that is limited in its rotation by surrounding bodystructures. A benefit of limiting the relative rotation of thebaseplates is that relative rotation beyond a certain range in a healthynatural disc is neither needed nor desired, because, for example, excessstrain can be placed on the facet joints or ligaments thereby. Asdescribed with the rotationally free embodiments of the third embodimentfamily, the construction also prevents translation and separation of thebaseplates relative to one another during rotation and angulation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a–c show top (FIG. 1 a), side cutaway (FIG. 1 b) and bottom(FIG. 1 c) views of a first baseplate of a first embodiment family ofthe present invention, the first baseplate having an inwardly directedradially compressible ball.

FIGS. 1 d–f show top (FIG. 1 d), side cutaway (FIG. 1 e) and bottom(FIG. 1 f) views of a second baseplate of the first embodiment family,the second baseplate having a circular recess within which seats aflexible convex structure.

FIGS. 1 g–h show side cutaway (FIG. 1 g) and top perspective (FIG. 1 h)views of a flexible convex structure of the first embodiment family, theflexible convex structure having spiral slots and radially extendinggrooves.

FIGS. 1 i–j show exploded (FIG. 1 i) and assembled (FIG. 1 j) views of apreferred embodiment of the first embodiment family.

FIGS. 2 a–c show top (FIG. 2 a), side cutaway (FIG. 2 b) and bottom(FIG. 2 c) views of a first baseplate of a second embodiment family ofthe present invention, the first baseplate having an inwardly directedradially compressible ball.

FIGS. 2 d–f show top (FIG. 2 d), side cutaway (FIG. 2 e) and bottom(FIG. 2 f) views of a second baseplate of the second embodiment family,the second baseplate having a curvate socket within which the ball iscapturable for free rotation and angulation therein.

FIGS. 2 g–h show exploded (FIG. 2 g) and assembled (FIG. 2 h) views of apreferred embodiment of the second embodiment family.

FIGS. 3 a–e show top (FIG. 3 a), side (FIG. 3 b), side cutaway (FIG. 3c), perspective cutaway (FIG. 3 d) and perspective (FIG. 3 e) views of afirst baseplate of a third embodiment family of the present invention.

FIGS. 3 f–j show top (FIG. 3 f), side (FIG. 3 g), side cutaway (FIG. 3h), perspective cutaway (FIG. 3 i) and perspective (FIG. 3 j) views of afirst type of a second baseplate of the third embodiment family, thefirst type of second baseplate having a convex structure of the thirdembodiment family integrated therewith.

FIGS. 3 k–o show top (FIG. 3 k), side (FIG. 3 l), side cutaway (FIG. 3m), perspective cutaway (FIG. 3 n) and perspective (FIG. 3 o) views of afirst type of a ball of the third embodiment family.

FIGS. 3 p–t show top (FIG. 3 p), side (FIG. 3 q), side cutaway (FIG. 3r), perspective cutaway (FIG. 3 s) and perspective (FIG. 3 t) views of afirst type of a cap of the third embodiment family.

FIGS. 3 u–y show top (FIG. 3 u), side (FIG. 3 v), side cutaway (FIG. 3w), perspective cutaway (FIG. 3 x) and perspective (FIG. 3 y) views ofan assembled first preferred embodiment of the third embodiment family.FIG. 3 z shows a side cutaway of an alternate assembled first preferredembodiment of the third embodiment family, having a bifurcated caphousing a spring member.

FIGS. 4 a–e show top (FIG. 4 a), side (FIG. 4 b), side cutaway (FIG. 4c), perspective cutaway (FIG. 4 d) and perspective (FIG. 4 e) views of asecond type of the second baseplate of the third embodiment family, thesecond type of the second baseplate having the convex structureintegrated therewith and also having a curvate recess.

FIGS. 4 f–j show top (FIG. 4 f), side (FIG. 4 g), side cutaway (FIG. 4h), perspective cutaway (FIG. 4 i) and perspective (FIG. 4 j) views of asecond type of the ball of the third embodiment family, the second typeof the ball having a protrusion.

FIGS. 4 k–o show top (FIG. 4 k), side (FIG. 4 l), side cutaway (FIG. 4m), perspective cutaway (FIG. 4 n) and perspective (FIG. 4 o) views of asecond type of a cap of the third embodiment family, the second type ofcap having a curvate recess.

FIGS. 4 p–t show top (FIG. 4 p), side (FIG. 4 q), side cutaway (FIG. 4r), perspective cutaway (FIG. 4 s) and perspective (FIG. 4 t) views ofan assembled second preferred embodiment of the third embodiment family.FIG. 4 u shows a side cutaway of an alternate assembled second preferredembodiment of the third embodiment family, having a bifurcated caphousing a spring member.

FIGS. 5 a–e show top (FIG. 5 a), side (FIG. 5 b), side cutaway (FIG. 5c), perspective cutaway (FIG. 5 d) and perspective (FIG. 5 e) views of athird type of the second baseplate of the third embodiment family, thethird type of the second baseplate having the convex structureintegrated therewith and also having a protrusion.

FIGS. 5 f–j show top (FIG. 5 f), side (FIG. 5 g), side cutaway (FIG. 5h), perspective cutaway (FIG. 5 i) and perspective (FIG. 5 j) views of athird type of the ball of the third embodiment family, the third type ofthe ball having a curvate recess.

FIGS. 5 k–o show top (FIG. 5 k), side (FIG. 5 l), side cutaway (FIG. 5m), perspective cutaway (FIG. 5 n) and perspective (FIG. 5 o) views ofan assembled third preferred embodiment of the third embodiment family.FIG. 5 p shows a side cutaway of an alternate assembled third preferredembodiment of the third embodiment family, having a bifurcated caphousing a spring member.

FIGS. 6 a–e show top (FIG. 6 a), side (FIG. 6 b), side cutaway (FIG. 6c), perspective cutaway (FIG. 6 d) and perspective (FIG. 6 e) views of afourth type of the second baseplate of the third embodiment family, thefourth type of the second baseplate having the convex structureintegrated therewith and also having a pin through hole for housing apin.

FIGS. 6 f–j show top (FIG. 6 f), side (FIG. 6 g), side cutaway (FIG. 6h), perspective cutaway (FIG. 6 i) and perspective (FIG. 6 j) views ofan assembled fourth preferred embodiment of the third embodiment family.FIG. 6 k shows a side cutaway of an alternate assembled fourth preferredembodiment of the third embodiment family, having a bifurcated caphousing a spring member.

FIGS. 7 a–e show top (FIG. 7 a), side (FIG. 7 b), side cutaway (FIG. 7c), perspective cutaway (FIG. 7 d) and perspective (FIG. 7 e) views of afifth type of the second baseplate of the third embodiment family, thefifth type of the second baseplate having the convex structureintegrated therewith and also having a recess.

FIGS. 7 f–j show top (FIG. 7 f), side (FIG. 7 g), side cutaway (FIG. 7h), perspective cutaway (FIG. 7 i) and perspective (FIG. 7 j) views ofan assembled fifth preferred embodiment of the third embodiment family.FIG. 7 k shows a side cutaway of an alternate assembled fifth preferredembodiment of the third embodiment family, having a bifurcated caphousing a spring member.

FIGS. 8 a–e show top (FIG. 8 a), side (FIG. 8 b), side cutaway (FIG. 8c), perspective cutaway (FIG. 8 d) and perspective (FIG. 8 e) views of afirst baseplate of a fourth embodiment family of the present invention.

FIGS. 8 f–j show top (FIG. 8 f), side (FIG. 8 g), side cutaway (FIG. 8h), perspective cutaway (FIG. 8 i) and perspective (FIG. 8 j) views of afirst type of second baseplate of the fourth embodiment family, thefirst type of the second baseplate having a central curvate pocket ofthe fourth embodiment family.

FIGS. 8 k–o show top (FIG. 8 k), side (FIG. 8 l), side cutaway (FIG. 8m), perspective cutaway (FIG. 8 n) and perspective (FIG. 8 o) views of afirst type of a ball of the fourth embodiment family.

FIGS. 8 p–t show top (FIG. 8 p), side (FIG. 8 q), side cutaway (FIG. 8r), perspective cutaway (FIG. 8 s) and perspective (FIG. 8 t) views of afirst type of a convex structure of the fourth embodiment family.

FIGS. 8 u–y show top (FIG. 8 u), side (FIG. 8 v), side cutaway (FIG. 8w), perspective cutaway (FIG. 8 x) and perspective (FIG. 8 y) views ofan assembled first preferred embodiment of the fourth embodiment family.FIG. 8 z shows a side cutaway of an alternate assembled first preferredembodiment of the fourth embodiment family, having a bifurcated secondbaseplate housing a spring member.

FIGS. 8 aa–8 dd illustrate an alternate embodiment of the presentinvention.

FIGS. 9 a–e show top (FIG. 9 a), side (FIG. 9 b), side cutaway (FIG. 9c), perspective cutaway (FIG. 9 d) and perspective (FIG. 9 e) views of asecond type of second baseplate of the fourth embodiment family, thesecond type of the second baseplate having the central curvate pocketand also having a curvate recess.

FIGS. 9 f–j show top (FIG. 9 f), side (FIG. 9 g), side cutaway (FIG. 9h), perspective cutaway (FIG. 9 i) and perspective (FIG. 9 j) views of asecond type of the ball of the fourth embodiment family, the second typeof the ball having a protrusion.

FIGS. 9 k–o show top (FIG. 9 k), side (FIG. 9 l), side cutaway (FIG. 9m), perspective cutaway (FIG. 9 n) and perspective (FIG. 9 o) views of asecond type of the convex structure of the fourth embodiment family, thesecond type of the convex structure having a curvate recess.

FIGS. 9 p–t show top (FIG. 9 p), side (FIG. 9 q), side cutaway (FIG. 9r), perspective cutaway (FIG. 9 s) and perspective (FIG. 9 t) views ofan assembled second preferred embodiment of the fourth embodimentfamily. FIG. 9 u shows a side cutaway of an alternate assembled secondpreferred embodiment of the fourth embodiment family, having abifurcated second baseplate housing a spring member.

FIGS. 10 a–e show top (FIG. 10 a), side (FIG. 10 b), side cutaway (FIG.10 c), perspective cutaway (FIG. 10 d) and perspective (FIG. 10 e) viewsof a third type of second baseplate of the fourth embodiment family, thethird type of the second baseplate having the central curvate pocket andalso having a recess on a circumferential wall around the curvatepocket.

FIGS. 10 f–j show top (FIG. 10 f), side (FIG. 10 g), side cutaway (FIG.10 h), perspective cutaway (FIG. 10 i) and perspective (FIG. 10 j) viewsof a third type of the ball of the fourth embodiment family, the thirdtype of the ball having a curvate recess.

FIGS. 10 k–o show top (FIG. 10 k), side (FIG. 10 l), side cutaway (FIG.10 m), perspective cutaway (FIG. 10 n) and perspective (FIG. 10 o) viewsof a third type of the convex structure of the fourth embodiment family,the third type of the convex structure having a protrusion.

FIGS. 10 p–t show top (FIG. 10 p), side (FIG. 10 q), side cutaway (FIG.10 r), perspective cutaway (FIG. 10 s) and perspective (FIG. 10 t) viewsof an assembled third preferred embodiment of the fourth embodimentfamily. FIG. 10 u shows a side cutaway of an alternate assembled thirdpreferred embodiment of the fourth embodiment family, having abifurcated second baseplate housing a spring member.

FIGS. 11 a–e show top (FIG. 11 a), side (FIG. 11 b), side cutaway (FIG.11 c), perspective cutaway (FIG. 11 d) and perspective (FIG. 11 e) viewsof a fourth type of the convex structure of the fourth embodimentfamily, the fourth type of the convex structure having a pin throughhole for housing a pin.

FIGS. 11 f–j show top (FIG. 11 f), side (FIG. 11 g), side cutaway (FIG.11 h), perspective cutaway (FIG. 11 i) and perspective (FIG. 11 j) viewsof an assembled fourth preferred embodiment of the fourth embodimentfamily. FIG. 11 k shows a side cutaway of an alternate assembled fourthpreferred embodiment of the fourth embodiment family, having abifurcated second baseplate housing a spring member.

FIGS. 12 a–e show top (FIG. 12 a), side (FIG. 12 b), side cutaway (FIG.12 c), perspective cutaway (FIG. 12 d) and perspective (FIG. 12 e) viewsof a fifth type of the convex structure of the fourth embodiment family,the fifth type of the convex structure having a recess adjacent acurvate taper.

FIGS. 12 f–j show top (FIG. 12 f), side (FIG. 12 g), side cutaway (FIG.12 h), perspective cutaway (FIG. 12 i) and perspective (FIG. 12 j) viewsof fourth type of ball of the fourth embodiment family, the fourth typeof ball having a curvate recess.

FIGS. 12 k–o show top (FIG. 12 k), side (FIG. 12 l), side cutaway (FIG.12 m), perspective cutaway (FIG. 12 n) and perspective (FIG. 12 o) viewsof an assembled fifth preferred embodiment of the fourth embodimentfamily. FIG. 12 p shows a side cutaway of an alternate assembled fifthpreferred embodiment of the fourth embodiment family, having abifurcated second baseplate housing a spring member.

FIG. 13 shows a side perspective view of a prior art interbody fusiondevice.

FIG. 14 shows a front view of the anterior portion of the lumbo-sacralregion of a human spine, into which a pair of interbody fusion devicesof FIG. 13 have been implanted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention will be described more fully hereinafter withreference to the accompanying drawings, in which particular embodimentsand methods of implantation are shown, it is to be understood at theoutset that persons skilled in the art may modify the invention hereindescribed while achieving the functions and results of the invention.Accordingly, the descriptions that follow are to be understood asillustrative and exemplary of specific structures, aspects and featureswithin the broad scope of the invention and not as limiting of suchbroad scope. Like numbers refer to similar features of like elementsthroughout.

A preferred embodiment of a first embodiment family of the presentinvention will now be described.

Referring to FIGS. 1 a–c, a first baseplate 10 of a first embodimentfamily of the present invention is shown in top (FIG. 1 a), side cutaway(FIG. 1 b) and bottom (FIG. 1 c) views. Also referring to FIGS. 1 d–f, asecond baseplate 30 of the first embodiment family is shown in top (FIG.1 d), side cutaway (FIG. 1 e) and bottom (FIG. 1 f) views.

More specifically, each baseplate 10, 30 has an outwardly facing surface12,32. Because the artificial disc of the invention is to be positionedbetween the facing surfaces of adjacent vertebral bodies, the twobaseplates 10,30 used in the artificial disc are disposed such that theoutwardly facing surfaces 12,32 face away from one another (as best seenin exploded view in FIG. 1 g and in assembly view in FIG. 1 h). The twobaseplates 10,30 are to mate with the vertebral bodies so as to notrotate relative thereto, but rather to permit the spinal segments tobend relative to one another in manners that mimic the natural motion ofthe spinal segment. This motion is permitted by the performance of aball and socket joint disposed between the secured baseplates 10,30. Themating of the baseplates 10,30 to the vertebral bodies and theconstruction of the ball and socket joint are described below.

More particularly, each baseplate 10, 30 is a flat plate (preferablymade of a metal such as, for example, cobalt-chromium or titanium)having an overall shape that conforms to the overall shape of therespective endplate of the vertebral body with which it is to mate.Further, each baseplate 10,30 comprises a vertebral body contact element(e.g., a convex mesh 14,34, preferably oval in shape) that is attachedto the outwardly facing surface 12,32 of the baseplate 10,30 to providea vertebral body contact surface. The mesh 14,34 is secured at itsperimeter to the outwardly facing surface 12,32 of the baseplate 10,30.The mesh 14,34 is domed in its initial undeflected conformation, butdeflects as necessary during insertion of the artificial disc betweenvertebral bodies, and, once the artificial disc is seated between thevertebral bodies, deforms as necessary under anatomical loads to reshapeitself to the concave surface of the vertebral endplate. This affordsthe baseplate 10,30 having the mesh 14,34 substantially superiorgripping and holding strength upon initial implantation as compared withother artificial disc products. The mesh 14,34 further provides anosteoconductive surface through which the bone may ultimately grow. Themesh 14,34 is preferably comprised of titanium, but can also be formedfrom other metals and/or non-metals without departing from the scope ofthe invention.

Each baseplate 10, 30 further comprises at least a lateral ring 16, 36that is osteoconductive, which may be, for example, a sprayed depositionlayer, or an adhesive applied beaded metal layer, or another suitableporous coating. This porous ring 16,36 permits the long-term ingrowth ofvertebral bone into the baseplate 10,30, thus permanently securing theprosthesis within the intervertebral space. It shall be understood thatthis porous layer 16,36 may extend beneath the domed mesh 14,34 as well,but is more importantly applied to the lateral rim of the outwardlyfacing surface 12,32 of the baseplate 10,30 that seats directly againstthe vertebral body.

As summarized above, each of the embodiments in the four embodimentfamilies discussed herein share the same basic elements, some of whichretain identical functionality and configuration across the embodiments,and some of which gain or lose functionality and/or configuration acrossthe embodiments to accommodate mechanical and/or manufacturingnecessities. More specifically, each of the embodiments has the twobaseplates joined to one another by a ball and socket joint that isestablished centrally between the baseplates. Each ball and socket jointis established by a socket being formed at the peak (or, in someembodiments, in the peak) of a convex structure extending from thesecond baseplate, and by a ball being secured to the first baseplate andbeing captured in the socket so that when the joint is placed under atension or compression force, the ball remains rotatably and angulatablysecure in the socket. However, the convex structure is configureddifferently in each of the embodiment families, and the manner in whichthe ball is captured in the socket is different in each of theembodiment families. Each of these two variations (the configuration ofthe convex structure and the manner of capturing the ball in the socket)among the embodiments families will be understood further in light ofthe detailed descriptions hereinbelow. It should be noted that althougheach of the embodiment families uses a preferred shape for the convexstructure (e.g., in the first and second embodiment families, thepreferred shape is frusto-conical, and in the third and fourthembodiment families, the preferred shape is a shape having a curvedtaper), the convex structure in each of the embodiment families is notlimited to a particular shape. For example, shapes including, but notlimited to, frusto-conical, hemispherical or semispherical shapes,shapes having sloped tapers or curved tapers, or shapes havingnon-uniform, irregular, or dimensionally varying tapers or contours,would also be suitable in any of the embodiment families.

In this regard, in this first embodiment family, the convex structure isconfigured as a flexible element and functions as a spring element thatprovides axial cushioning to the device. The convex structure has thesocket of the ball and socket joint at its peak. In order to permit theflexible convex structure to flex under compressive loads applied to thedevice, it is a separate element from the second baseplate. In thepreferred embodiment, the flexible convex structure is a bellevillewasher that has a frusto-conical shape. Other flexible convex structuresare also contemplated as being suitable, such as, for example, convexstructures that flex because of the resilience of the material fromwhich they are made, because of the shape into which they are formed,and/or or because of the mechanical interaction between sub-elements ofan assembly forming the convex structure. Although the convex structureis a separate element from the second baseplate in this embodimentfamily (so that it is able to flex), it is preferably maintained nearthe second baseplate so that the device does not separate in tension.Therefore, an extension of the second baseplate is provided (in the formof a shield element) to cover enough of the convex structure to somaintain it. Stated alternatively, the shield is a separate element fromthe second baseplate to ease manufacturing (during assembly, theflexible convex structure is first placed against the second baseplate,and then the shield is placed over the convex structure and secured tothe second baseplate so that the convex structure is maintained betweenthe second baseplate and the shield), but once the device is assembled,the second baseplate and the shield are effectively one element. Thatis, the second baseplate and shield can be considered to be a singleintegral housing within which the separate flexible convex structureflexes, because but for the sake of achieving desirable manufacturingefficiencies, the second baseplate and shield would be one piece.

Also in this regard, in the first embodiment family, the manner ofcapturing the ball in the socket is effected by the ball beingselectively radially compressible. That is, the ball is radiallycompressed to fit into the socket and thereafter receives a deflectionpreventing element to prevent subsequent radial compression, so that theball remains captured in the socket. A more detailed description of thepreferred manner in which this is accomplished is described below.Because the socket is formed at the peak of the flexible convexstructure discussed immediately above, the capturing of the ball in thesocket in this manner allows the ball to remain securely held forrotation and angulation even though the socket moves upward and downwardwith the flexing of the convex structure. The second baseplatepreferably includes an access hole that accommodates placement of thedeflection preventing element, so that the same can be applied to theball after the ball is fitted into the socket. Accordingly, the ball ismaintained in the socket.

More specifically, in this preferred embodiment of the first embodimentfamily, with regard to joining the two baseplates 10,30 with a ball andsocket joint, each of the baseplates 10,30 comprises features that, inconjunction with other components described below, form the ball andsocket joint. More specifically, the first baseplate 10 includes aninwardly facing surface 18 that includes a perimeter region 20 and aball 22 mounted to protrude from the inwardly facing surface 18. Theball 22 preferably has a semispherical shape defining a sphericalcontour. The ball 22 includes a series of slots 24 that render the ball22 radially compressible and expandable in correspondence with a radialpressure (or a radial component of a pressure applied thereto andreleased therefrom). The ball 22 further includes an axial bore 26 thataccepts a deflection preventing element (e.g., rivet, plug, dowel, orscrew; a rivet 28 is used herein as an example) (shown in FIGS. 1 i–j).(Alternatively, the axial bore can be threaded to accept a screw.) Priorto the insertion of the rivet 28, the ball 22 can deflect radiallyinward because the slots 24 will narrow under a radial pressure. Theinsertion of the rivet 28 eliminates the capacity for this deflection.Therefore, the ball 22, before receiving the rivet 28, can be compressedto pass into, and thereafter seat in, a central curvate socket of aconvex structure (described below). Once the ball 22 has been seated inthe curvate socket, the rivet 28 can be inserted into the axial bore 26to ensure that the ball 22 remains held in the curvate socket. Asdescribed below, an access hole is preferably provided in the secondbaseplate 30 so that the interior of the device may be readily accessedfor inserting the rivet 28 into the axial bore 26, or for otherpurposes.

The second baseplate 30 includes an inwardly facing surface 38 thatincludes a perimeter region 40 and a central circular recess 42 withinwhich the wide end of the convex structure resides, and a pair of holes44 through which rivets 46 (shown in FIGS. 1 g–h) may be provided forsecuring a shield element 48 that is placed over the convex structure,which shield 48 thus serves as an extension of the second baseplate 30(the shield 48 is more fully set forth below with and shown on FIGS. 1i–j).

Referring now to FIGS. 1 g–h, the convex structure 31 that resides inthe circular recess 42 is shown in side cutaway (FIG. 1 g) and topperspective (FIG. 1 h) views. In this embodiment, the convex structure31 is frusto-conical and is flexible. Because the convex structure 31 isflexible, it functions as a force restoring element (e.g., a spring)that provides axial cushioning to the device, by deflecting under acompressive load and restoring when the load is relieved. The flexibleconvex structure 31 is preferably, as shown, a belleville washer thathas a frusto-conical shape. The belleville washer 31 preferably, asshown, has spiral slots and radially extending grooves. The restoringforce of the belleville washer 31 is proportional to the elasticproperties of the material or materials from which it is made. It shouldbe understood that belleville washers having the configuration shown canbe used with the present invention, but that belleville washers havingother conformations, that is, without or without slots and/or grooves,and/or with other groove and slots configurations, including the same ordifferent numbers of grooves and/or slots, can also be used with and areencompassed by the present invention.

The belleville washer 31 comprises a series of spiral slots 33 formedtherein. The slots 33 extend from the outer edge of the bellevillewasher 31, inward along arcs generally directed toward the center of theelement. The slots 33 do not extend fully to the center of the element.Preferably, the slots 33 extend anywhere from a quarter to threequarters of the overall radius of the washer 31, depending upon therequirements of the patient, and the anatomical requirements of thedevice.

The belleville washer 31 further comprises a series of grooves 35 formedtherein. The grooves 35 extend radially from the outer edge of thebelleville washer 31 toward the center of the element. Preferably, thewidth and depth of each groove 35 decreases along the length of thegroove 35 from the outer edge of the washer 31 toward the center of thewasher 31, such that the center of the washer 31 is flat, while theouter edge of the washer 31 has grooves of a maximum groove depth. Itshould be understood that in other embodiments, one or both of the depthand the width of each groove can be (1) increasing along the length ofthe groove from the outer edge of the washer toward the center of thewasher, (2) uniform along the length of the groove from the outer edgeof the washer toward the center of the washer, or (3) varied along thelength of each groove from the outer edge of the washer toward thecenter of the washer, either randomly or according to a pattern.Moreover, in other embodiments, it can be the case that each groove isnot formed similarly to one or more other grooves, but rather one ormore grooves are formed in any of the above-mentioned fashions, whileone or more other grooves are formed in another of the above-mentionedfashions or other fashions. It should be clear that any groove patterncan be implemented without departing from the scope of the presentinvention, including, but not limited to, at least one radially spacedconcentric groove, including, but not limited to, at least one suchgroove having at least one dimension that varies along the length of thegroove. Belleville washers having circumferential extents that radiallyvary in at least one dimension, are also contemplated by the presentinvention.

As a compressive load is applied to the belleville washer 31, the forcesare directed into a hoop stress which tends to radially expand thewasher 31. This hoop stress is counterbalanced by the material strengthof the washer 31, and the force necessary to widen the spiral slots 33and the radial grooves 35 along with the strain of the material causes adeflection in the height of the washer 31. Stated equivalently, thebelleville washer 31 responds to a compressive load by deflectingcompressively; the spiral slots and/or radial grooves cause the washerto further respond to the load by spreading as the slots and/or thegrooves in the washer expand under the load. The spring, therefore,provides a restoring force which is proportional to the elastic modulusof the material in a hoop stressed condition.

With regard to the above discussion regarding the curvate socket thatreceives the ball 22 of the first baseplate 10, the curvate socket isformed at the peak of the convex structure 31. The curvate socket 37 isprovided inasmuch as the central opening of the belleville washer 31 isenlarged. This central opening includes a curvate volume 37 forreceiving therein the ball 22 of the first baseplate 10. Moreparticularly, the curvate volume 37 has a substantially constant radiusof curvature that is also substantially equivalent to the radius of theball 22. In this embodiment, the spiral slots 33 of the washer 31 do notextend all the way to the central opening, and approach the opening onlyas far as the material strength of the washer 31 can handle withoutplastically deforming under the expected anatomical loading. Further inthis embodiment, the depth of each groove 35 of the washer 31 decreasesalong the length of the groove 35 from the outer edge of the washer 31toward the center of the washer 31, such that the center of the washer31 is flat, while the outer edge of the washer 31 has grooves of amaximum groove depth. Therefore, the central opening can be formed fromflat edges. It should be understood that this is not required, butrather is preferred for this embodiment.

The curvate socket 37 has an opening diameter that accommodates passagetherethrough of the ball 22 in a radially compressed state (but not inan uncompressed state), and a larger inner diameter that accommodatesthe ball 22 in the uncompressed state. Therefore, the ball 22 can beradially compressed to pass into the curvate socket 37 under force, andthen will radially expand to the uncompressed state once in the curvatesocket 37. Once the rivet 28 is then secured into the axial bore 26, therivet 28 prevents the ball 22 from radially compressing, and thereforethe ball 22 cannot back out through the opening. An access hole 39 inthe second baseplate 30 below the curvate socket 37 has a diameter thataccommodates the diameter of the rivet 28 and thereby provides easyaccess to insert the rivet 28 in the axial bore 26 after the ball 22 hasbeen seated in the curvate socket 37. To prevent the ball 22 fromescaping the curvate socket 37 through the second baseplate 30, thediameter of the access hole 39 is smaller than the inner diameter of thecurvate socket 37.

The curvate socket 37 defines a spherical contour that closelyaccommodates the ball 22 for free rotation and angulation in itsuncompressed state. Therefore, when seated in the curvate socket 37, theball 22 can rotate and angulate freely relative to the curvate socket 37through a range of angles, thus permitting the opposing baseplates 10,30to rotate and angulate freely relative to one another through acorresponding range of angles equivalent to the fraction of normal humanspine rotation and angulation (to mimic normal disc rotation andangulation). Further preferably, the perimeter regions 20,40 havecorresponding contours, so that the meeting of the perimeter regions20,40 as a result of the angulation of the baseplates 10,30 reduces anysurface wearing.

Referring to FIGS. 1 i–j, exploded (FIG. 1 i) and assembled (FIG. 1 i)views of the preferred embodiment of the first embodiment family areshown. Included in these views are the shield 48 and the correspondingrivets 46. More particularly, assembly of the disc is preferably asfollows. The first and second baseplates 10,30 are disposed so thattheir outwardly facing surfaces 12,32 face away from one another andtheir inwardly facing surfaces 18,38 are directed toward one another.The convex structure 31 is then positioned with its wide end in thecircular recess 42 of the second baseplate, so that the curvate socket37 of the convex structure 31 is aligned with the ball 22 of the firstbaseplate 10. Then, the shield 48 is secured over the belleville washer31 (the shield 48 is preferably frusto-conical to follow the shape ofthe belleville washer 31, although other shield shapes are suitable andcontemplated by the present invention) by passing the central hole 41 ofthe shield 48 over the curvate socket 37 and applying the rivets 46through rivet holes 43 in the shield 48 and into the rivet holes 44 inthe second baseplate 30. Then, the ball 22 is pressed into the curvatesocket 37 under a force sufficient to narrow the slots 24 and therebyradially compress the ball 22 until the ball 22 fits through and passesthrough the opening of the curvate socket 37. Once the ball 22 is insidethe curvate socket 37, the ball 22 will radially expand as the slots 24widen until it has returned to its uncompressed state and the sphericalcontour defined by the ball 22 is closely accommodated by the sphericalcontour defined by the curvate socket 37 and the ball 22 can rotate andangulate freely relative to the curvate socket 37. Thereafter, the rivet28 is passed through the access hole 39 and pressed into the axial bore26 of the ball 22 to prevent any subsequent radially compression of theball 22 and therefore any escape from the curvate socket 37 thereby.Because the diameter of the circular recess 42 is greater than thediameter of the wide end of the belleville washer 31, compressiveloading of the device (and therefore the belleville washer) can resultin an unrestrained radial deflection of the belleville washer 31. Thespiral slots 33 and radial grooves 35 of the belleville washer 31enhance this deflection. When the load is removed, the belleville washer31 springs back to its original shape.

Accordingly, when the device of the preferred embodiment of the firstembodiment family is assembled, the baseplates 10,30 are rotatablerelative to one another because the ball 22 rotates freely within thecurvate socket 37, and angulatable relative to one another because theball 22 angulates freely within the socket 37. Because the convexstructure 31 is flexible (and is housed in the second baseplate 30 in amanner that permits it to flex), the baseplates 10,30 are also axiallycompressible relative to one another. Because the ball 22 is held withinthe curvate socket 37 by a rivet 28 in the axial bore 26 preventingradial compression of the ball 22, the artificial disc can withstandtension loading of the baseplates 10,30. More particularly, when atension load is applied to the baseplates 10,30, the ball 22 in thecurvate socket 37 seeks to radially compress to fit through the openingof the curvate socket 37. However, the rivet 28 in the axial bore 26 ofthe ball 22 prevents the radial compression, thereby preventing the ball22 from exiting the curvate socket 37. Therefore, the assembly does notcome apart under normally experienced tension loads. This ensures thatno individual parts of the assembly will pop out or slip out frombetween the vertebral bodies when, e.g., the patient stretches or hangswhile exercising or performing other activities. Thus, in combinationwith the securing of the baseplates 10,30 to the adjacent vertebralbones via the mesh domes 14,34, the disc assembly has an integritysimilar to the tension-bearing integrity of a healthy naturalintervertebral disc. Also, because the ball 22 is laterally captured inthe curvate socket 37, lateral translation of the baseplates 10,30relative to one another is prevented during rotation and angulation,similar to the performance of healthy natural intervertebral disc.Because the baseplates 10,30 are made angulatable relative to oneanother by the ball 22 being rotatably and angulatably coupled in thecurvate socket 37, the disc assembly provides a centroid of motionwithin the ball 22. Accordingly, the centroid of motion of the discassembly remains centrally located between the vertebral bodies, similarto the centroid of motion in a healthy natural intervertebral disc.

A preferred embodiment of a second embodiment family of the presentinvention will now be described.

Referring to FIGS. 2 a–c, a first baseplate 50 of a second embodimentfamily of the present invention is shown in top (FIG. 2 a), side cutaway(FIG. 2 b) and bottom (FIG. 2 c) views. Also referring to FIGS. 2 d–f, asecond baseplate 70 of the second embodiment family is shown in top(FIG. 2 d), side cutaway (FIG. 2 e) and bottom (FIG. 2 f) views.

With regard to the configuration of the convex structure in this secondembodiment family, and the manner in which the ball is captured in thesocket in this second embodiment family, the convex structure isconfigured as a non-flexible element that is integral with the secondbaseplate, and has the socket of the ball and socket joint at its peak.More clearly stated, the devices of this second embodiment family do notfeature a flexible convex structure, and therefore (and also because ofthe manner in which the ball is captured in this second embodimentfamily, discussed immediately below) there is no need for the convexstructure to be a separate element from the second baseplate. (Bycontrast, in the first embodiment family, as discussed above, becausethe convex structure is flexible, it is separated from the secondbaseplate so that it is able to flex.) In the preferred embodiment, theconvex structure has a frusto-conical shape. The manner of capturing theball in the socket in this second embodiment family is identical to thatof the first embodiment family.

More specifically, the first and second baseplates 50,70 are similar tothe first and second baseplates 10,30 of the first embodiment familydescribed above with regard to each outwardly facing surface 52,72having a vertebral body contact element 54,74 and an adjacentosteoconductive ring 56,76, and each inwardly facing surface 58,78having a perimeter region 60,80, all of which elements in the secondembodiment family are, for example, identical to the correspondingelements in the first embodiment family as described above.

Further, as with the first embodiment family, the two baseplates 50,70are joined with a ball and socket joint, and therefore each of thebaseplates 50,70 comprises features that, in conjunction with othercomponents described below, form the ball and socket joint. Morespecifically, the first baseplate 50 is formed similarly to the firstbaseplate 10 of the first embodiment family, having a ball 62 mounted toprotrude from the inwardly facing surface 58. The ball 62 preferably hasa semispherical shape defining a spherical contour. The ball 62 isstructurally and functionally identical to the ball 22 of the firstembodiment family, and as such is selectively radially compressible inthe same manner as the ball 22 of the first embodiment family. As withthe ball 22 of the first embodiment family, the ball 62 is capturable ina curvate socket 77 formed at the peak of a convex structure 71protruding from the second baseplate 70. The curvate socket 77 isfunctionally and structurally identical to the curvate socket 37 of thefirst embodiment family. However, in this second embodiment family, theconvex structure 77 of the device, rather than being a flexible separateelement from the second baseplate as in the first embodiment family, isintegral with the second baseplate 70. The convex structure 77 isfrusto-conical, but is not flexible, and therefore does not function asa force restoring element as does the flexible convex structure 37 inthe first embodiment family. Access to the convex structure 77 forproviding easy access to insert the rivet 68 in the axial bore 66 of theball 62 after the ball 62 has been seated in the curvate socket 77 isprovided by an access hole 79 in the second baseplate 70 below andleading to the curvate socket 77. The access hole 79 is otherwisestructurally identical to the access hole 39 in the second baseplate 30of the first embodiment family.

Referring to FIGS. 2 g–h, an assembled preferred embodiment of thesecond embodiment family is shown in exploded (FIG. 2 g) and assembled(FIG. 2 h) views. More particularly, assembly of the disc is preferablyas follows. The first and second baseplates 50,70 are disposed so thattheir outwardly facing surfaces 52,72 face away from one another andtheir inwardly facing surfaces 58,78 are directed toward one another,and so that the ball 62 of the first baseplate 50 is aligned with thecurvate socket 77 of the convex structure 71 of the second baseplate 70.Then, the ball 62 is pressed into the curvate socket 77 under a forcesufficient to narrow the slots 64 and thereby radially compress the ball62 until the ball 62 fits through and passes through the opening of thecurvate socket 77. Once the ball 62 is inside the curvate socket 77, theball 62 will radially expand as the slots 64 widen until it has returnedto its uncompressed state and the spherical contour defined by the ball62 is closely accommodated by the spherical contour defined by thecurvate socket 77 and the ball 62 can rotate and angulate freelyrelative to the curvate socket 77. Thereafter, the rivet 68 is passedthrough the access hole 79 and pressed into the axial bore 66 of theball 62 to prevent any subsequent radially compression of the ball 62and therefore any escape from the curvate socket 77 thereby.

Accordingly, when the device of the preferred embodiment of the secondembodiment family is assembled, the baseplates 50,70 are rotatablerelative to one another because the ball 62 rotates freely within thecurvate socket 77, and angulatable relative to one another because theball 62 angulates freely within the socket 77. Because the ball 62 isheld within the curvate socket 77 by a rivet 68 in the axial bore 66preventing radial compression of the ball 62, the artificial disc canwithstand tension loading of the baseplates 50,70. More particularly,when a tension load is applied to the baseplates 50,70, the ball 62 inthe curvate socket 77 seeks to radially compress to fit through theopening of the curvate socket 77. However, the rivet 68 in the axialbore 66 of the ball 62 prevents the radial compression, therebypreventing the ball 62 from exiting the curvate socket 77. Therefore,the assembly does not come apart under normally experienced tensionloads. This ensures that no individual parts of the assembly will popout or slip out from between the vertebral bodies when, e.g., thepatient stretches or hangs while exercising or performing otheractivities. Thus, in combination with the securing of the baseplates50,70 to the adjacent vertebral bones via the mesh domes 54,74, the discassembly has an integrity similar to the tension-bearing integrity of ahealthy natural intervertebral disc. Also because the ball 62 islaterally captured in the curvate socket 77, lateral translation of thebaseplates 50,70 relative to one another is prevented during rotationand angulation, similar to the performance of healthy naturalintervertebral disc. Because the baseplates 50,70 are made angulatablerelative to one another by the ball 62 being rotatably and angulatablycoupled in the curvate socket 77, the disc assembly provides a centroidof motion within the ball 62. Accordingly, the centroid of motion of thedisc assembly remains centrally located between the vertebral bodies,similar to the centroid of motion in a healthy natural intervertebraldisc.

Embodiments of the third embodiment family of the present invention willnow be described.

With regard to the configuration of the convex structure in the thirdembodiment family, the convex structure is configured as a non-flexibleelement that is integral with the second baseplate, and has the socketof the ball and socket joint at its peak, similar to the configurationof the convex structure in the second embodiment family. In thepreferred embodiment, the convex structure is shaped to have a curvedtaper.

With regard to the manner in which the ball is captured in the socket inthe third embodiment family, the capturing is effected through the useof a solid ball. In order to permit the seating of the ball into thesocket formed at the peak of the convex structure, the access hole inthe second baseplate has a diameter that accommodates the diameter ofthe ball, and leads to the interior of the peak, which interior isformed as a concavity having an opening diameter that accommodates thediameter of the ball. (Preferably, the concavity has a curvature closelyaccommodating the contour of the ball, and the concavity is eitherhemispherical or less-than-hemispherical so that the ball can easily beplaced into it.) Further, in order to maintain the ball in the socket,an extension of the second baseplate (in the form of a cap element) isprovided for sealing the access hole in the second baseplate (orreducing the opening diameter of the hole to a size that does notaccommodate the diameter of the ball). The cap has an interior face thatpreferably has a concavity (that has a curvature that closelyaccommodates the contour of the ball) to complete the socket. The peakof the convex structure has a bore that accommodates a post to which theball and the first baseplate are attached (one to each end of the post),but does not accommodate the ball for passage through the bore.Accordingly, the ball is maintained in the socket.

A first preferred embodiment of a third embodiment family of the presentinvention will now be described.

Referring to FIGS. 3 a–e, a first baseplate 100 of the third embodimentfamily of the present invention is shown in top (FIG. 3 a), side (FIG. 3b), side cutaway (FIG. 3 c), perspective cutaway (FIG. 3 d) andperspective (FIG. 3 e) views. Also referring to FIGS. 3 f–j, a firsttype 200 of a second baseplate of the third embodiment family is shownin top (FIG. 3 f), side (FIG. 3 g), side cutaway (FIG. 3 h), perspectivecutaway (FIG. 3 i) and perspective (FIG. 3 j) views.

More specifically, the first and second baseplates 100,200 are similarto the first and second baseplates 50,70 of the second embodiment familydescribed above with regard to each having an outwardly facing surface102,202, and each inwardly facing surface 108,208 having a perimeterregion 110,210, all of which elements in the third embodiment familyare, for example, identical to the corresponding elements in the firstembodiment family as described above. However, each of the first andsecond baseplates 100,200 in this second embodiment family instead ofhaving a convex mesh as a vertebral body contact element, have a convexsolid dome 103,203 and a plurality of spikes 105,205 as vertebral bodycontact element. Preferably, the dome 103,203 is covered with anosteoconductive layer of a type known in the art. It should be notedthat the convex solid dome 203 of the second baseplate 200 is providedin this embodiment (and the other embodiments in this family) by the capelement (described below) that serves as an extension of the secondbaseplate 200 to capture the ball (described below), as best shown inFIGS. 3 u–y. It should also be noted that the convex mesh used in otherembodiments of the present invention is suitable for use with theseother vertebral body contact elements, and can be attached over theconvex dome 103,203 by laser welding, or more preferably, by plasmaburying (where the perimeter region of the convex mesh is buried under aplasma coating, which coating secures to the outwardly facing surface ofthe baseplate to which it is applied, and thus secures the convex meshto the outwardly facing surface).

Further, as with the first embodiment family, the two baseplates 100,200are joined with a ball and socket joint, and therefore each of thebaseplates 100,200 comprises features that, in conjunction with othercomponents described below, form the ball and socket joint. The ball andsocket joint includes a solid ball (described below) mounted to protrudefrom the inwardly facing surface 108 of the first baseplate 100, and acurvate socket formed at a peak of a non-flexible convex structure(described below) that is integral with the second baseplate 200, withinwhich curvate socket the ball is capturable for free rotation andangulation therein. As shown in FIGS. 3 a–e, the mounting for the ballincludes a central hole 112 on the inwardly facing surface 108 of thefirst baseplate 100, which hole 112 accepts a tail end of a post(described below) that has the ball at a head end of the post.Preferably, the tail end compression locks into the hole 112. As shownin FIGS. 3 f–j, the convex structure 201 is integral with the secondbaseplate 200 and includes a curvate pocket 212 formed by a centralportion of the inwardly facing surface 209 of the convex structure 201convexing inwardly and by a central portion of an outwardly facingsurface 213 of the convex structure 201 concaving inwardly. The pocket212 has a semispherical contour on the central portion of the outwardlyfacing surface 213 and an apex at the center of the semisphericalcontour. Further, the convex structure 201 has a bore 214 through theapex of the pocket 212, to accommodate the post. Further, the secondbaseplate 200 has on its outwardly facing surface 202 an access hole 209surrounded by a circular recess 216 leading to the pocket 212, whichrecess 216 accepts the cap (described below) that serves as an extensionof the second baseplate 200.

Referring now to FIGS. 3 k–o, a first type 300 of the ball of the thirdembodiment family is shown in top (FIG. 3 k), side (FIG. 3 l), sidecutaway (FIG. 3 m), perspective cutaway (FIG. 3 n) and perspective (FIG.3 o) views. The ball 300 is mounted at a head end 306 of a post 302 thatalso has a tail end 304. The ball 300 defines a spherical contour thatis interrupted by the shaft of the post 302.

Referring now to FIGS. 3 p–t, a first type 400 of the cap of the thirdembodiment family is shown in top (FIG. 3 p), side (FIG. 3 q), sidecutaway (FIG. 3 r), perspective cutaway (FIG. 3 s) and perspective (FIG.3 t) views. The cap 400 includes an outwardly facing surface 402 thatcomplements the outwardly facing surface 202 of the second baseplate 200when the cap 400 is secured in the circular recess 216 of the secondbaseplate 200 (preferably, as shown, the outwardly facing surface 402 ofthe cap 400 provides the second baseplate 200 with the convex dome 203,as best shown in FIGS. 3 u–y). The cap 400 further includes an inwardlyfacing surface 404, and a curvate pocket 406 formed by a central portionof the inwardly facing surface 404 of the cap 400 concaving outwardly.The pocket 406 has a semispherical contour that closely accommodates thespherical contour defined by the ball 300. The semispherical contour ofthe pocket 406 of the cap 400 opposes the semispherical contour of thepocket 212 of the convex structure 201 such that when the cap 400 issecured in the circular recess 216 of the second baseplate 200, thesemispherical contours together define a socket 207 defining a sphericalcontour that closely accommodates the spherical contour defined by theball 300 for free rotation and angulation of the ball 300 in the pockets406,212. Each of the semispherical contour of the pocket 406 and thesemispherical contour of the pocket 212 are preferably no greater thanhemispherical, to make easier the assembly of the device.

Referring now to FIGS. 3 u–y, an assembled first preferred embodiment ofthe third embodiment family is shown in top (FIG. 3 u), side (FIG. 3 v),side cutaway (FIG. 3 w), perspective cutaway (FIG. 3 x) and perspective(FIG. 3 y) views. More particularly, assembly of the disc is preferablyas follows. The tail end 304 of the post 302 is passed through theaccess hole 209 in the second baseplate 200 and through the bore 214 atthe apex of the curvate pocket 212 of the convex structure 201, and thetail end 304 is thereafter secured to the central hole 112 in the firstbaseplate 100. (The access hole 209 has a diameter that accommodates thediameter of the ball 300 at the head 306 of the post 302, and thecurvate pocket 212 on the outwardly facing surface 213 of the convexstructure 201 has an opening diameter that accommodates the ball 300 forseating in the pocket 212 when the tail end 304 is fully passed throughthe bore 214. Thus, the ball 300 can be placed through the access hole209 and into the curvate pocket during this step.) The bore 214 at theapex of the curvate pocket 212 has a diameter greater than the diameterof the post 302 but smaller than the diameter of the ball 300 at thehead 306 of the post 302. Therefore, as the ball 300 is being placedinto the curvate pocket 212, the post 302 fits through the bore 214, butthe ball 300 does not, and the convex structure 201 (and the secondbaseplate 200) cannot be freed from the ball 300 once the tail end 304of the post 302 is secured to the first baseplate 100. Although anysuitable method is contemplated by the present invention, the attachmentof the tail end 304 of the post 302 is preferably accomplished bycompression locking (if accomplished alternatively or additionally bylaser welding, the laser weld can, e.g., be applied from the outwardlyfacing surface 102 of the first baseplate 100 if the hole 112 passescompletely through the first baseplate 100). The tail end 304 can alsoalternatively or additionally be threaded into the central hole 112 forincreased stability of the attachment.

The semispherical contour of the pocket 212 closely accommodates thespherical contour defined by the ball 300, so that the ball 300 canfreely rotate in the pocket 212 about the longitudinal axis of the post302, and can freely angulate in the pocket 212 about a centroid ofmotion located at the center of the ball 300. Further, the bore 214 istapered to a larger diameter toward the first baseplate 100, to permitthe post 302 to angulate (about the centroid of motion at the center ofthe ball 300) with respect to the bore 214 as the ball 300 angulates inthe pocket 212. Preferably, the conformation of the taper accommodatesangulation of the post 302 at least until the perimeter regions 110,210of the inwardly facing surfaces 108,208/211 meet.

Finally, the cap 400 is secured in the circular recess 216 of the secondbaseplate 200, so that the curvate pocket 406 of the cap 400 and theopposing curvate pocket 212 of the convex structure 201 together formthe socket 207 defining the spherical contour within which the ball 300at the head 306 of the post 302 freely rotates and angulates asdescribed above. The application of the cap 400 also seals the accesshole 209 in the second baseplate (or, if the cap 400 has a bore, itpreferably reduces the diameter of the access hole 209 to a size thatdoes not accommodate the diameter of the ball 300). Although anysuitable method is contemplated by the present invention, the cap 400preferably is secured in the circular recess 216 by compression locking(a laser weld can alternatively or additionally be used, or othersuitable attachment means). As stated above, the cap 400 preferably hasan outwardly facing surface 402 that complements the outwardly facingsurface 202 of the second baseplate 200 for surface uniformity once thecap 400 is secured. The cap 400 may also additionally or alternativelybe threaded into the circular recess 216 for increased stability of theattachment.

Referring now to FIG. 3 z, an assembled alternate first preferredembodiment of the third embodiment family is shown in side cutaway view.This alternate first preferred embodiment incorporates a multi-part cap(with first part 4000 a and second part 4000 b) housing a spring member4100 that provides axial compressibility, such that a compressive loadapplied to the baseplates is borne by the spring member 4100. Elementsof this alternate first preferred embodiment that are also elementsfound in the first preferred embodiment are like numbered, and theassembly of this alternate first preferred embodiment is identical tothat of the first preferred embodiment, with some differences due to theincorporation of the spring member 4100. (For example, the cap featuresare numbered in the 4000's rather than the 400's.) More particularly,assembly of the disc is preferably as follows. The tail end 304 of thepost 302 is passed through the access hole 209 in the second baseplate200 and through the bore 214 at the apex of the curvate pocket 212 ofthe convex structure 201, and the tail end 304 is thereafter secured tothe central hole 112 in the first baseplate 100. (The access hole 209has a diameter that accommodates the diameter of the ball 300 at thehead 306 of the post 302, and the curvate pocket 212 on the outwardlyfacing surface 213 of the convex structure 201 has an opening diameterthat accommodates the ball 300 for seating in the pocket 212 when thetail end 304 is fully passed through the bore 214. Thus, the ball 300can be placed through the access hole 209 and into the curvate pocketduring this step.) The bore 214 at the apex of the curvate pocket 212has a diameter greater than the diameter of the post 302 but smallerthan the diameter of the ball 300 at the head 306 of the post 302.Therefore, as the ball 300 is being placed into the curvate pocket 212,the post 302 fits through the bore 214, but the ball 300 does not, andthe convex structure 201 (and the second baseplate 200) cannot be freedfrom the ball 300 once the tail end 304 of the post 302 is secured tothe first baseplate 100. Although any suitable method is contemplated bythe present invention, the attachment of the tail end 304 of the post302 is preferably accomplished by compression locking (if accomplishedalternatively or additionally by laser welding, the laser weld can,e.g., be applied from the outwardly facing surface 102 of the firstbaseplate 100 if the hole 112 passes completely through the firstbaseplate 100). The tail end 304 can also alternatively or additionallybe threaded into the central hole 112 for increased stability of theattachment.

The semispherical contour of the pocket 212 closely accommodates thespherical contour defined by the ball 300, so that the ball 300 canfreely rotate in the pocket 212 about the longitudinal axis of the post302, and can freely angulate in the pocket 212 about a centroid ofmotion located at the center of the ball 300. Further, the bore 214 istapered to a larger diameter toward the first baseplate 100, to permitthe post 302 to angulate (about the centroid of motion at the center ofthe ball 300) with respect to the bore 214 as the ball 300 angulates inthe pocket 212. Preferably, the conformation of the taper accommodatesangulation of the post 302 at least until the perimeter regions 110,210of the inwardly facing surfaces 108,208/211 meet.

The second part 4000 b of the multi-part cap is secured in the circularrecess 216 of the second baseplate 200, so that the curvate pocket 4060of the inwardly facing surface 4040 b of the cap second part 4000 b andthe opposing curvate pocket 212 of the convex structure 201 togetherform the socket 207 defining the spherical contour within which the ball300 at the head 306 of the post 302 freely rotates and angulates asdescribed above. The application of the cap second part 4000 b (and thecap first part 4000 a) also seals the access hole 209 in the secondbaseplate (or, if the cap second and first parts 4000 b, 4000 a havebores, it preferably reduces the diameter of the access hole 209 to asize that does not accommodate the diameter of the ball 300). The capsecond part 4000 b is preferably not compressed into, but rather fitsloosely within the boundaries of, the circular recess 216, so that whenthe first baseplate 100 is compressed toward the second baseplate 200,the cap second part 4000 b may travel toward the cap first part 4000 aas the spring member 4100 compresses (due to the cap first part 4000 abeing secured in the circular recess 216 to the second baseplate 200).The spring member 4100 is then disposed on the outwardly facing surface4020 b of the cap second part 4000 b. While not limited to anyparticular structure, assembly, or material, a spring member providingshock absorption preferably includes an elastomeric material, such as,for example, polyurethane or silicon, and a spring member providingshock dampening preferably includes a plastic material, such as, forexample, polyethylene. It should be understood that metal springs mayalternatively or additionally be used. The illustrated spring member4100 is formed of an elastomeric material, for example. The illustratedspring member 4100 is ring-shaped, for example, such that it fits justinside the circumferential edge of the outwardly facing surface 4020 bof the cap second part 4000 b as shown.

Finally, the cap first part 4000 a is secured in the circular recess 216of the second baseplate 200 to incarcerate the cap second part 4000 b,and the spring member 4100 between the outwardly facing surface 4020 bof the cap second part 4000 b and the inwardly facing surface 4040 a ofthe cap first part 4000 a. Although any suitable method is contemplatedby the present invention, the cap first part 4000 a preferably issecured in the circular recess 216 by compression locking (a laser weldcan alternatively or additionally be used, or other suitable attachmentmeans). The cap second part 4000 b should be dimensioned such that, andthe spring member 4100 should have an uncompressed height such that, agap is present between the outwardly facing surface 4020 b of the capsecond part 4000 b and the inwardly facing surface 4040 a of the capfirst part 4000 a when the disc is assembled. The gap preferably has aheight equivalent to the anticipated distance that the spring member4100 will compress under an anticipated load. The cap first part 4000 apreferably has an outwardly facing surface 4020 a that complements theoutwardly facing surface 202 of the second baseplate 200 for surfaceuniformity once the cap first part 4000 a is secured. The cap first part4000 a may also additionally or alternatively be threaded into thecircular recess 216 for increased stability of the attachment.Accordingly, in this alternate first preferred embodiment, part or allof a compressive load applied to the baseplates will be borne by thespring member 4100, which will dampen the load and/or absorb the loadand preferably help return the baseplates to their original uncompressedrelative positions.

Accordingly, when a device of the first preferred embodiment of thethird embodiment family is assembled, the baseplates are rotatablerelative to one another because the ball 300 rotates freely within thesocket 207, and angulatable relative to one another because the ball 300angulates freely within the socket 207. Because the ball 300 is heldwithin the socket 207 by the securing of the tail end 304 of the post302 to the first baseplate 100 and the securing of the cap 400 (or capfirst part 4000 a) to the second baseplate 200, the artificial disc canwithstand tension loading of the baseplates 100,200. More particularly,when a tension load is applied to the baseplates 100,200 the ball 300seeks to pass through the bore 214 at the apex of the curvate pocket212. However, the smaller diameter of the bore 214 relative to thediameter of the ball 300 prevents the ball 300 from exiting the socket207. Therefore, the assembly does not come apart under normallyexperienced tension loads. This ensures that no individual parts of theassembly will pop out or slip out from between the vertebral bodieswhen, e.g., the patient stretches or hangs while exercising orperforming other activities. Thus, in combination with the securing ofthe baseplates 100,200 to the adjacent vertebral bones via the domes103,203 and spikes 105,205, the disc assembly has an integrity similarto the tension-bearing integrity of a healthy natural intervertebraldisc. Also because the ball 300 is laterally captured in the socket 207,lateral translation of the baseplates 100,200 relative to one another isprevented during rotation and angulation, similar to the performance ofhealthy natural intervertebral disc. Because the baseplates 100,200 aremade angulatable relative to one another by the ball 300 being rotatablyand angulatably coupled in the socket 207, the disc assembly provides acentroid of motion within the ball 300. Accordingly, the centroid ofmotion of the disc assembly remains centrally located between thevertebral bodies, similar to the centroid of motion in a healthy naturalintervertebral disc.

The remaining embodiments in the third embodiment family of the presentinvention limit the rotation (but preferably not the angulation) of theball in the socket defined by the pocket of the convex structure and thepocket of the cap. Each embodiment accomplishes this in a differentmanner, but each embodiment utilizes interference between a protrusionand a recess to limit the rotation. In some embodiments, the protrusionis preferably hemispherical, and the recess preferably has asemicylindrical contour within which the protrusion fits. In otherembodiments, the protrusion is preferably hemispherical, and the recesspreferably has a curvate contour that is not semicylindrical. (It shouldbe understood that the described formations of the recess and theprotrusion are merely preferred, and that alternate formations, curvateor otherwise, for each are contemplated by the present invention; aparticular shape or location of recess or a particular shape or locationof protrusion is not required; any shape can be used so long as therecess and protrusion interact as desired. For example, the recess inthe second preferred embodiment of the third embodiment family has acurvate contour that is not semicylindrical so that it optimallyinteracts with the protrusion in that embodiment.) The boundaries of therecess define the limits of rotation of the ball within the socket, byallowing movement of the protrusion relative to the recess as the ballrotates through a certain range in the socket, but providinginterference with the protrusion to prevent rotation of the ball beyondthat range in the socket. Preferably, for example, the recess has adepth equivalent to the radius of the protrusion, but a radius ofcurvature greater than that of the protrusion. At the same time, theboundaries of the recess preferably do not limit the angulation of theball within the socket, at least until the perimeter regions of theinwardly facing surfaces meet. Preferably for example, the recess has alength greater than the range of movement of the protrusion relative tothe recess as the ball angulates in the socket.

Therefore, when assembled, the discs of the remaining preferredembodiments of the third embodiment family enable angulation and limitedrotation of the baseplates relative to one another about a centroid ofmotion that remains centrally located between the baseplates (at thecenter of the sphere defined by the ball), similar to the centroid ofmotion in a healthy natural intervertebral disc that is limited in itsrotation by surrounding body structures. A benefit of limiting therelative rotation of the baseplates is that relative rotation beyond acertain range in a healthy natural disc is neither needed nor desired,because, for example, excess strain can be placed on the facet joints orligaments thereby. As described with the first preferred embodiment ofthe third embodiment family, the construction also prevents translationand separation of the baseplates relative to one another during rotationand angulation.

As noted above, each of the remaining preferred embodiments in thisthird embodiment family forms the protrusion and corresponding recess ina different manner, utilizing components that are either identical orsimilar to the components of the first preferred embodiment, and someembodiments utilize additional components. Each of the remainingpreferred embodiments will now be described in greater detail.

In the second preferred embodiment of the third embodiment family of thepresent invention, a hemispherical protrusion is formed on the ballitself, and interacts in the above-described manner with a curvaterecess formed adjacent the socket defined by the pocket of the convexstructure and the pocket of the cap. More particularly, this secondpreferred embodiment uses the same first baseplate 100 as the firstpreferred embodiment of the third embodiment family described above.Referring to FIGS. 4 a–e, a second type 500 of second baseplate of thethird embodiment family is shown in top (FIG. 4 a), side (FIG. 4 b),side cutaway (FIG. 4 c), perspective cutaway (FIG. 4 d) and perspective(FIG. 4 e) views. This second type 500 of second baseplate is identicalto the first type 200 of second baseplate described above (and thussimilar features are reference numbered similar to those of the firsttype 200 of second baseplate, but in the 500s rather than the 200s),except that this second type 500 of second baseplate has a curvaterecess 518 adjacent the curvate pocket 512 in the convex structure 501.

As shown in FIGS. 4 a to 4 e, the convey structure 501 is integral withthe second baseplate 500 and includes a curvate pocket 512 formed by acentral portion 511 of the inwardly-facing surface 508 of the convexstructure 501 convexing inwardly and by a central portion of anoutwardly-facing surface 513 of the convex structure 501 concavinginwardly. The pocket 512 has a semispherical contour on the centralportion of the outwardly-facing surface 513 and an apex at the center ofthe semispherical contour. Further, the convex structure 501 has a bore514 through the apex of the pocket 512, to accommodate the post.Further, the second baseplate 500 has an outwardly-facing surface 502and an access hole 509 surrounded by a circular recess 516 leading tothe pocket 512, which recess 216 accepts the cap that serves as anextension of the baseplate. The convex structure 501 also includes aperimeter region 510 extending about the inwardly-facing surface 508. Aplurality of spikes 505 may also be included on the outwardly-facingsurface 502 of baseplate 500.

Referring now to FIGS. 4 f–j, a second type 600 of ball of the thirdembodiment family is shown in top (FIG. 4 f), side (FIG. 4 g), sidecutaway (FIG. 4 h), perspective cutaway (FIG. 4 i) and perspective (FIG.4 j) views. The ball 600 is identical to the first type 300 of balldescribed above (and thus similar features are reference numberedsimilar to those of the first type 300 of ball, but in the 600s ratherthan the 300s), except that the spherical contour defined by this secondtype 600 of ball is also interrupted by a hemispherical protrusion 608.Thus, ball 600 includes a post 602 having a tail end 604 disposed at oneend and a head 606 disposed opposite the tail end.

Referring now to FIGS. 4 k–o, a second type 700 of cap of the thirdembodiment family is shown in top (FIG. 4 k), side (FIG. 4 l), sidecutaway (FIG. 4 m), perspective cutaway (FIG. 4 n) and perspective (FIG.4 o) views. This second type 700 of cap is identical to the first type400 of cap described above (and thus similar features are referencenumbered similar to those of the first type 400 of cap, but in the 700srather than the 400s), except that this second type 700 of cap has acurvate recess 708 adjacent the curvate pocket 706. Cap 700, similar tocap 400, also includes an outwardly-facing surface 702 and aninwardly-facing surface 704. As with regard to cap 400, outwardly-facingsurface 702 compliments the outwardly-facing surface 502 of baseplate500 to provide surface uniformity once the cap 700 is secured.

Referring now to FIGS. 4 p–t, an assembled second preferred embodimentof the third embodiment family is shown in top (FIG. 4 p), side (FIG. 4q), side cutaway (FIG. 4 r), perspective cutaway (FIG. 4 s) andperspective (FIG. 4 t) views. It can be seen that the curvate recesses518,708 together form the recess described above in the discussion ofthe manner in which these remaining embodiments limit rotation of theball in the socket, and that the protrusion 608 serves as the protrusiondescribed above in the same discussion. Thus, the protrusion 608 andrecesses 518,708 interact in the above described manner to limit therotation of the ball 600 in the socket 507 defined by the curvatepockets 512,706. Assembly of the disc is identical to that of the firstpreferred embodiment of the third embodiment family, except that theprotrusion 608 is longitudinally aligned with the recess 518, and therecess 708 is similarly aligned, so that when the cap 700 is secured tothe second baseplate 500, the protrusion 608 is fitted within therecesses 518,708 for interaction as described above as the ball 600rotates and angulates in the socket 507.

Referring now to FIG. 4 u, an assembled alternate second preferredembodiment of the third embodiment family is shown in side cutaway view.This alternate second preferred embodiment incorporates a multi-part cap(with first part 7000 a and second part 7000 b) housing a spring member7100 that provides axial compressibility, such that a compressive loadapplied to the baseplates is borne by the spring member 7100. Elementsof this alternate second preferred embodiment that are also elementsfound in the second preferred embodiment are like numbered. (The capfeatures are numbered in the 7000's rather than the 700's.) The curvaterecesses 518,7080 together form the recess described above, and theprotrusion 608 serves as the protrusion described above, and thus theprotrusion 608 and the recesses 518,7080 interact in the above describedmanner to limit the rotation of the ball 600 in the socket 507 definedby the curvate pockets 512,7060.

Assembly of this alternate second preferred embodiment is identical tothat of the alternate first preferred embodiment of the third embodimentfamily, except that the protrusion 608 is longitudinally aligned withthe recess 518, and the recess 7080 is similarly aligned, so that whenthe cap second part 7000 b is disposed in the circular recess 516 of thesecond baseplate 500, the protrusion 608 is fitted within the recesses518,7080 for interaction as described above as the ball 600 rotates andangulates in the socket 507. The cap second part 7000 b is preferablynot compressed into, but rather fits loosely within, the circular recess516, so that when the first baseplate 100 is compressed toward thesecond baseplate 500, the cap second part 7000 b may travel toward thecap first part 7000 a as the spring member 7100 compresses (due to thecap first part 7000 a being secured in the circular recess 516 to thesecond baseplate 500). The spring member 7100 is then disposed on theoutwardly facing surface 7020 b of the cap second part 7000 b. While notlimited to any particular structure, assembly, or material, a springmember providing shock absorption preferably includes an elastomericmaterial, such as, for example, polyurethane or silicon, and a springmember providing shock dampening preferably includes a plastic material,such as, for example, polyethylene. It should be understood that metalsprings may alternatively or additionally be used. The illustratedspring member 7100 is formed of an elastomeric material, for example.The illustrated spring member 7100 is ring-shaped, for example, suchthat it fits just inside the circumferential edge of the outwardlyfacing surface 7020 b of the cap second part 7000 b as shown.

Finally, the cap first part 7000 a is secured in the circular recess 516of the second baseplate 500 to incarcerate the cap second part 7000 b,and the spring member 7100 between the outwardly facing surface 7020 bof the cap second part 7000 b and the inwardly facing surface 7040 a ofthe cap first part 7000 a. Although any suitable method is contemplatedby the present invention, the cap first part 7000 a preferably issecured in the circular recess 516 by compression locking (a laser weldcan alternatively or additionally be used, or other suitable attachmentmeans). The cap second part 7000 b should be dimensioned such that, andthe spring member 7100 should have an uncompressed height such that, agap is present between the outwardly facing surface 7020 b of the capsecond part 7000 b and the inwardly facing surface 7040 a of the capfirst part 7000 a when the disc is assembled. The gap preferably has aheight equivalent to the anticipated distance that the spring member7100 will compress under an anticipated load. The cap first part 7000 apreferably has an outwardly facing surface 7020 a that complements theoutwardly facing surface 502 of the second baseplate 500 for surfaceuniformity once the cap first part 7000 a is secured. The cap first part7000 a may also additionally or alternatively be threaded into thecircular recess 516 for increased stability of the attachment.Accordingly, in this alternate first preferred embodiment, part or allof a compressive load applied to the baseplates will be borne by thespring member 7100, which will dampen the load and/or absorb the loadand preferably help return the baseplates to their original uncompressedrelative positions.

In the third preferred embodiment of the third embodiment family of thepresent invention, a hemispherical protrusion is formed to protrude intothe socket defined by the pocket of the convex structure and the pocketof the cap, and interacts in the above-described manner with asemicylindrical recess formed on the ball. More particularly, this thirdpreferred embodiment uses the same first baseplate 100 and the same cap400 as the first preferred embodiment of the third embodiment family.Referring to FIGS. 5 a–e, a third type 800 of second baseplate of thethird embodiment family is shown in top (FIG. 5 a), side (FIG. 5 b),side cutaway (FIG. 5 c), perspective cutaway (FIG. 5 d) and perspective(FIG. 5 e) views. This third type 800 of second baseplate is identicalto the first type 200 of second baseplate described above (and thussimilar features are reference numbered similar to those of the firsttype 200 of second baseplate, but in the 800s rather than the 200s),except that this third type 800 of second baseplate has a protrusion 818jutting out from the wall of the pocket 812 in the convex structure 801.

As shown in FIGS. 5 a to 5 e, the convex structure 801 is integral withthe second baseplate 800 and includes a curvate pocket 812 formed by acentral portion 811 of the inwardly-facing surface 808 of the convexstructure 801 convexing inwardly and by a central portion of anoutwardly-facing surface 813 of the convex structure 801 concurvinginwardly. The inwardly-facing surface 808 also includes a perimeterregion 801. The pocket 812 has a semispherical contour on the centralportion on the outwardly-facing surface 813 and an apex at the center ofthe semispherical contour. Further, the convex structure 801 has a bore814 extending through the apex of the pocket 812, to accommodate thepost. Further, baseplate 800 has an outwardly-facing surface 802 and anaccess hole 809 surrounded by a circular recess 816 leading to thepocket 812, which recess 816 accepts the cap 9 described below) thatserves as an extension of the baseplate 800. The baseplate 800preferably also includes a plurality of spikes 805 disposed along theoutwardly-facing surface 802. As shown in FIG. 5 n, cap 400 can besecured to the circular recess 816 and provide a convex dome 803 tobaseplate 800.

Referring now to FIGS. 5 f–j, a third type 900 of ball of the thirdembodiment family is shown in top (FIG. 5 f), side (FIG. 5 g), sidecutaway (FIG. 5 h), perspective cutaway (FIG. 5 i) and perspective (FIG.5 j) views. The ball 900 is identical to the first type 300 of balldescribed above (and thus similar features are reference numberedsimilar to those of the first type 300 of ball, but in the 900s ratherthan the 300s), except that the spherical contour of this third type 900of ball is also interrupted by a curvate recess 908. As with previousembodiments ball 900 includes a post 902 having a tail end 904 and ahead end 906.

Referring now to FIGS. 5 k–o, an assembled third preferred embodiment ofthe third embodiment family is shown in top (FIG. 5 k), side (FIG. 5 l),side cutaway (FIG. 5 m), perspective cutaway (FIG. 5 n) and perspective(FIG. 5 o) views. It can be seen that the curvate recess 908 forms therecess described above in the discussion of the manner in which theseremaining embodiments limit rotation of the ball in the socket, and thatthe protrusion 818 serves as the protrusion described above in the samediscussion. Thus, the protrusion 818 and recess 908 interact in theabove described manner to limit the rotation of the ball 900 in thesocket 807 defined by the curvate pockets 812,406. Assembly of the discis identical to that of the first preferred embodiment of the thirdembodiment family, except that the protrusion 818 is longitudinallyaligned with the recess 908 during assembly so that the protrusion 818is fitted within the recess 908 for interaction as described above asthe ball 900 rotates and angulates in the socket 807.

Referring now to FIG. 5 p, an assembled alternate third preferredembodiment of the third embodiment family is shown in side cutaway view.This alternate third preferred embodiment incorporates a multi-part cap(with first part 4000 a and second part 4000 b) housing a spring member4100 that provides axial compressibility, such that a compressive loadapplied to the baseplates is borne by the spring member 4100. Elementsof this alternate third preferred embodiment that are also elementsfound in the third preferred embodiment are like numbered. (The capfeatures are numbered in the 4000's rather than the 400's.) The curvaterecess 908 forms the recess described above, and the protrusion 818serves as the protrusion described above, and thus the protrusion 818and the recess 908 interact in the above described manner to limit therotation of the ball 900 in the socket 807 defined by the curvatepockets 812,4060.

Assembly of this alternate third preferred embodiment is identical tothat of the alternate first preferred embodiment of the third embodimentfamily, except that the protrusion 818 is longitudinally aligned withthe recess 908 during assembly so that the protrusion 818 is fittedwithin the recess 908 for interaction as described above as the ball 900rotates and angulates in the socket 807. The cap second part 4000 b ispreferably not compressed into, but rather fits loosely within, thecircular recess 816, so that when the first baseplate 100 is compressedtoward the second baseplate 800, the cap second part 4000 b may traveltoward the cap first part 4000 a as the spring member 4100 compresses(due to the cap first part 4000 a being secured in the circular recess816 to the second baseplate 800). The spring member 4100 is thendisposed on the outwardly facing surface 4020 b of the cap second part4000 b. While not limited to any particular structure, assembly, ormaterial, a spring member providing shock absorption preferably includesan elastomeric material, such as, for example, polyurethane or silicon,and a spring member providing shock dampening preferably includes aplastic material, such as, for example, polyethylene. It should beunderstood that metal springs may alternatively or additionally be used.The illustrated spring member 4100 is formed of an elastomeric material,for example. The illustrated spring member 4100 is ring-shaped, forexample, such that it fits just inside the circumferential edge of theoutwardly facing surface 4020 b of the cap second part 4000 b as shown.

Finally, the cap first part 4000 a is secured in the circular recess 816of the second baseplate 800 to incarcerate the cap second part 4000 b,and the spring member 4100 between the outwardly facing surface 4020 bof the cap second part 4000 b and the inwardly facing surface 4040 a ofthe cap first part 4000 a. Although any suitable method is contemplatedby the present invention, the cap first part 4000 a preferably issecured in the circular recess 816 by compression locking (a laser weldcan alternatively or additionally be used, or other suitable attachmentmeans). The cap second part 4000 b should be dimensioned such that, andthe spring member 4100 should have an uncompressed height such that, agap is present between the outwardly facing surface 4020 b of the capsecond part 4000 b and the inwardly facing surface 4040 a of the capfirst part 4000 a when the disc is assembled. The gap preferably has aheight equivalent to the anticipated distance that the spring member4100 will compress under an anticipated load. The cap first part 4000 apreferably has an outwardly facing surface 4020 a that complements theoutwardly facing surface 802 of the second baseplate 800 for surfaceuniformity once the cap first part 4000 a is secured. The cap first part4000 a may also additionally or alternatively be threaded into thecircular recess 816 for increased stability of the attachment.Accordingly, in this alternate first preferred embodiment, part or allof a compressive load applied to the baseplates will be borne by thespring member 4100, which will dampen the load and/or absorb the loadand preferably help return the baseplates to their original uncompressedrelative positions.

In the fourth preferred embodiment of the third embodiment family of thepresent invention, a pin is secured in a pin hole so that thehemispherical head of the pin protrudes into the socket defined by thepocket of the convex structure and the pocket of the cap, and interactsin the above-described manner with a semicylindrical recess formed onthe ball. More particularly, this fourth preferred embodiment uses thesame first baseplate 100 and cap 400 of the first preferred embodiment,and the same ball 900 of the third preferred embodiment, but utilizes afourth type of second baseplate of the third embodiment family.Referring to FIGS. 6 a–e, the fourth type 1000 of second baseplate isshown in top (FIG. 6 a), side (FIG. 6 b), side cutaway (FIG. 6 c),perspective cutaway (FIG. 6 d) and perspective (FIG. 6 e) views. Thisfourth type 1000 of second baseplate is identical to the first type 200of second baseplate described above (and thus similar features arereference numbered similar to those of the first type 200 of secondbaseplate, but in the 1000s rather than the 200s), except that thisfourth type 1000 of second baseplate has a lateral through hole (e.g., apin hole 1020) and a protrusion (e.g., a pin 1018) secured in the pinhole 1020 (as shown in FIGS. 6 f–j) with the hemispherical head of thepin 1018 jutting out from the wall of the pocket 1012 toward the centerof the pocket 1012 in the convex structure 1001.

As shown in FIGS. 6 a to 6 e, second baseplate 1000 similar to secondbaseplate 200, includes convex structure 1001 integral with secondbaseplate 1000 and includes a curvate pocket 1012 formed by a centralportion 1011 of the inwardly-facing surface 1008 of the convex structure1001 convexing inwardly and by a central portion of an outwardly-facingsurface 1013 of the convex structure 1001 concaving inwardly. Theinwardly-facing surface 1008 also includes a perimeter region 1010extending about the inwardly-facing surface. The pocket 1012 has asemispherical contour on the central portion of the outwardly-facingsurface 1012 and an apex at the center of the semispherical contour.Further, the convex structure 1001 has a bore 1014 extending through theapex of the pocket 1012 to accommodate the post. Further, the secondbaseplate 1000 has on its outwardly-facing surface 1002 an access hole1009 surrounded by a circular recess 1016 leading to the pocket 1012,which recess 1016 accepts the cap as previously described in conjunctionwith previous embodiments. In one preferred embodiment, the secondbaseplate 1000 includes a plurality of spikes 1005 disposed along itsoutwardly-facing surface 1002. As best seen in FIG. 6 i, cap 400 may besecured in the circular recess 1016 of the baseplate 1000 and preferablyincludes a convex dome 1003 similar to convex dome 203.

Referring now to FIGS. 6 f–j, an assembled fourth preferred embodimentof the third embodiment family is shown in top (FIG. 6 f), side (FIG. 6g), side cutaway (FIG. 6 h), perspective cutaway (FIG. 6 i) andperspective (FIG. 6 j) views. It can be seen that the curvate recess 908of the ball 900 forms the recess described above in the discussion ofthe manner in which these remaining embodiments limit rotation of theball in the socket, and that the head of the pin 1018 serves as theprotrusion described above in the same discussion. Thus, the head of thepin 1018 and the recess 908 interact in the above described manner tolimit the rotation of the ball 900 in the socket 1007 defined by thecurvate pockets 1012,406. Assembly of the disc is identical to that ofthe first preferred embodiment of the third embodiment family, exceptthat the head of the pin 1018 is longitudinally aligned with the recess908 during assembly so that the head of the pin 1018 is fitted withinthe recess 908 for interaction as described above as the ball 900rotates and angulates in the socket 1007.

Referring now to FIG. 6 k, an assembled alternate fourth preferredembodiment of the third embodiment family is shown in side cutaway view.This alternate fourth preferred embodiment incorporates a multi-part cap(with first part 4000 a and second part 4000 b) housing a spring member4100 that provides axial compressibility, such that a compressive loadapplied to the baseplates is borne by the spring member 4100. Elementsof this alternate fourth preferred embodiment that are also elementsfound in the fourth preferred embodiment are like numbered. (The capfeatures are numbered in the 4000's rather than the 400's.) The curvaterecess 908 of the ball 900 forms the recess described above, and thehead of the pin 1018 serves as the protrusion described above, and thusthe head of the pin 1018 and the recess 908 interact in the abovedescribed manner to limit the rotation of the ball 900 in the socket1007 defined by the curvate pockets 1012,4060.

Assembly of this alternate fourth preferred embodiment is identical tothat of the alternate first preferred embodiment of the third embodimentfamily, except that the head of the pin 1018 is longitudinally alignedwith the recess 908 during assembly so that the head of the pin 1018 isfitted within the recess 908 for interaction as described above as theball 900 rotates and angulates in the socket 1007. The cap second part4000 b is preferably not compressed into, but rather fits looselywithin, the circular recess 1016, so that when the first baseplate 100is compressed toward the second baseplate 1000, the cap second part 4000b may travel toward the cap first part 4000 a as the spring member 4100compresses (due to the cap first part 4000 a being secured in thecircular recess 1016 to the second baseplate 1000). The spring member4100 is then disposed on the outwardly facing surface 4020 b of the capsecond part 4000 b. While not limited to any particular structure,assembly, or material, a spring member providing shock absorptionpreferably includes an elastomeric material, such as, for example,polyurethane or silicon, and a spring member providing shock dampeningpreferably includes a plastic material, such as, for example,polyethylene. It should be understood that metal springs mayalternatively or additionally be used. The illustrated spring member4100 is formed of an elastomeric material, for example. The illustratedspring member 4100 is ring-shaped, for example, such that it fits justinside the circumferential edge of the outwardly facing surface 4020 bof the cap second part 4000 b as shown.

Finally, the cap first part 4000 a is secured in the circular recess1016 of the second baseplate 1000 to incarcerate the cap second part4000 b, and the spring member 4100 between the outwardly facing surface4020 b of the cap second part 4000 b and the inwardly facing surface4040 a of the cap first part 4000 a. Although any suitable method iscontemplated by the present invention, the cap first part 4000 apreferably is secured in the circular recess 1016 by compression locking(a laser weld can alternatively or additionally be used, or othersuitable attachment means). The cap second part 4000 b should bedimensioned such that, and the spring member 4100 should have anuncompressed height such that, a gap is present between the outwardlyfacing surface 4020 b of the cap second part 4000 b and the inwardlyfacing surface 4040 a of the cap first part 4000 a when the disc isassembled. The gap preferably has a height equivalent to the anticipateddistance that the spring member 4100 will compress under an anticipatedload. The cap first part 4000 a preferably has an outwardly facingsurface 4020 a that complements the outwardly facing surface 1002 of thesecond baseplate 1000 for surface uniformity once the cap first part4000 a is secured. The cap first part 4000 a may also additionally oralternatively be threaded into the circular recess 1016 for increasedstability of the attachment. Accordingly, in this alternate firstpreferred embodiment, part or all of a compressive load applied to thebaseplates will be borne by the spring member 4100, which will dampenthe load and/or absorb the load and preferably help return thebaseplates to their original uncompressed relative positions.

In the fifth preferred embodiment of the third embodiment family of thepresent invention, a ball bearing protrudes into the socket defined bythe pocket of the convex structure and the pocket of the cap, andinteracts in the above-described manner with a semicylindrical recessformed on the ball. More particularly, this fifth preferred embodimentuses the same first baseplate 100 and cap 400 of the first preferredembodiment, and the same ball 900 of the third preferred embodiment, bututilizes a fifth type of second baseplate of the third embodimentfamily. Referring to FIGS. 7 a–e, the fifth type 1200 of secondbaseplate is shown in top (FIG. 7 a), side (FIG. 7 b), side cutaway(FIG. 7 c), perspective cutaway (FIG. 7 d) and perspective (FIG. 7 e)views. This fifth type 1200 of second baseplate is identical to thefirst type 200 of second baseplate described above (and thus similarfeatures are reference numbered similar to those of the first type 200of second baseplate, but in the 1200s rather than the 200s), except thatthis fifth type 1200 of second baseplate has a recess 1218 adjacent thecurvate pocket 1212 in the convex structure 1201, the recess 1218preferably being semicylindrical as shown.

As shown in FIGS. 7 a to 7 e, second baseplate 1200 is similarlydesigned to baseplate 200 and includes a convex structure 1201 integralwith the second baseplate 1200 and includes a curvate pocket 1212 formedby a central portion 1211 of the inwardly-facing surface 1208 of theconvex structure 1201 convexing inwardly and by a central portion of anoutwardly-facing surface 1213 of convex structure 1201 concavinginwardly. The inwardly-facing surface 1208 preferably includes aperimeter region 1210 extending about its surface. The pocket 1212 has asemispherical contour of the central portion of the outwardly-facingsurface 1213 and an apex at the center of the semispherical contour.Further, the convex structure 1201 has a bore 1214 through the apex ofthe pocket 1212, which recess 1216 accepts the cap 400. As best seen inFIG. 7 i, cap 400 when received within recess 1216 provides a convexdome 1203 to the second baseplate, as described with reference to secondbaseplate 200. In one preferred embodiment, baseplate 1200 includes aplurality of spikes 1205 extending from outwardly-facing surface 1202.

Referring now to FIGS. 7 f–j, an assembled fifth preferred embodiment ofthe third embodiment family is shown in top (FIG. 7 f), side (FIG. 7 g),side cutaway (FIG. 7 h), perspective cutaway (FIG. 7 i) and perspective(FIG. 7 j) views. A ball bearing 1300 of the third embodiment family iscaptured for free rotation and angulation with one part closelyaccommodated in the semicylindrical recess 1218 and one part protrudinginto the curvate pocket 1212 to interact with the curvate recess 908 ofthe ball 900. It can be seen that the curvate recess 908 of the ball 900forms the recess described above in the discussion of the manner inwhich these remaining embodiments limit rotation of the ball in thesocket, and that the ball bearing 1300 serves as the protrusiondescribed above in the same discussion. Thus, the ball bearing 1300 andthe recess 908 interact in the above described manner to limit therotation of the ball 900 in the socket 1207 defined by the curvatepockets 1212,406. Assembly of the disc is identical to that of the firstpreferred embodiment of the third embodiment family, except that thesemicylindrical recess 1218 is longitudinally aligned with the curvaterecess 908 during assembly so that the ball bearing 1300 can be and isthen placed into the recesses 1218,908 for interaction as describedabove as the ball 900 rotates and angulates in the socket 1207.

Referring now to FIG. 7 k, an assembled alternate fifth preferredembodiment of the third embodiment family is shown in side cutaway view.This alternate fifth preferred embodiment incorporates a multi-part cap(with first part 4000 a and second part 4000 b) housing a spring member4100 that provides axial compressibility, such that a compressive loadapplied to the baseplates is borne by the spring member 4100. Elementsof this alternate fourth preferred embodiment that are also elementsfound in the fourth preferred embodiment are like numbered. (The capfeatures are numbered in the 4000's rather than the 400's.) The curvaterecess 908 of the ball 900 forms the recess described above, and theball bearing 1300 serves as the protrusion described above, and thus theball bearing 1300 and the recess 908 interact in the above describedmanner to limit the rotation of the ball 900 in the socket 1207 definedby the curvate pockets 1212,4060.

Assembly of this alternate fifth preferred embodiment is identical tothat of the alternate first preferred embodiment of the third embodimentfamily, except that the semicylindrical recess 1218 is longitudinallyaligned with the curvate recess 908 during assembly so that the ballbearing 1300 can be and is then placed into the recesses 1218,908 forinteraction as described above as the ball 900 rotates and angulates inthe socket 1207. The cap second part 4000 b is preferably not compressedinto, but rather fits loosely within, the circular recess 1216, so thatwhen the first baseplate 100 is compressed toward the second baseplate1200, the cap second part 4000 b may travel toward the cap first part4000 a as the spring member 4100 compresses (due to the cap first part4000 a being secured in the circular recess 1216 to the second baseplate1200). The spring member 4100 is then disposed on the outwardly facingsurface 4020 b of the cap second part 4000 b. While not limited to anyparticular structure, assembly, or material, a spring member providingshock absorption preferably includes an elastomeric material, such as,for example, polyurethane or silicon, and a spring member providingshock dampening preferably includes a plastic material, such as, forexample, polyethylene. It should be understood that metal springs mayalternatively or additionally be used. The illustrated spring member4100 is formed of an elastomeric material, for example. The illustratedspring member 4100 is ring-shaped, for example, such that it fits justinside the circumferential edge of the outwardly facing surface 4020 bof the cap second part 4000 b as shown.

Finally, the cap first part 4000 a is secured in the circular recess1216 of the second baseplate 1200 to incarcerate the cap second part4000 b, and the spring member 4100 between the outwardly facing surface4020 b of the cap second part 4000 b and the inwardly facing surface4040 a of the cap first part 4000 a. Although any suitable method iscontemplated by the present invention, the cap first part 4000 apreferably is secured in the circular recess 1216 by compression locking(a laser weld can alternatively or additionally be used, or othersuitable attachment means). The cap second part 4000 b should bedimensioned such that, and the spring member 4100 should have anuncompressed height such that, a gap is present between the outwardlyfacing surface 4020 b of the cap second part 4000 b and the inwardlyfacing surface 4040 a of the cap first part 4000 a when the disc isassembled. The gap preferably has a height equivalent to the anticipateddistance that the spring member 4100 will compress under an anticipatedload. The cap first part 4000 a preferably has an outwardly facingsurface 4020 a that complements the outwardly facing surface 1202 of thesecond baseplate 1200 for surface uniformity once the cap first part4000 a is secured. The cap first part 4000 a may also additionally oralternatively be threaded into the circular recess 1216 for increasedstability of the attachment. Accordingly, in this alternate firstpreferred embodiment, part or all of a compressive load applied to thebaseplates will be borne by the spring member 4100, which will dampenthe load and/or absorb the load and preferably help return thebaseplates to their original uncompressed relative positions.

Embodiments of the fourth embodiment family of the present inventionwill now be described.

With regard to the configuration of the convex structure in the fourthembodiment family, the convex structure is configured as a non-flexibleelement that has the socket of the ball and socket joint at its peak. Inthe preferred embodiment, the convex structure is shaped to have acurved taper, similar to the configuration of the convex structure inthe third embodiment family. The convex structure in the fourthembodiment family is separated from the second baseplate during assemblyof the device, for reasons related to the manner in which the ball iscaptured in the socket, but is attached to the second baseplate by thetime assembly is complete.

With regard to the manner in which the ball is captured in the socket inthe fourth embodiment family, the capturing is effected through the useof a solid ball. In order to permit the seating of the ball into thesocket formed at the peak of the convex structure, the convex structureis a separate element from the second baseplate. The ball is firstseated against the central portion of the second baseplate (whichcentral portion preferably has a concavity that has a curvature thatclosely accommodates the contour of the ball), and then the convexstructure is placed over the ball to seat the ball in the socket formedin the interior of the peak of the convex structure (the interior ispreferably formed as a concavity that is either hemispherical orless-than-hemispherical so that the ball can easily fit into it). Afterthe convex structure is placed over the ball, the convex structure isattached to the second baseplate to secure the ball in the socket. As inthe third embodiment family, the peak of the convex structure has a borethat accommodates a post to which the ball and the first baseplate areattached (one to each end of the post), but does not accommodate theball for passage through the bore. Accordingly, the ball is maintainedin the socket.

A first preferred embodiment of a fourth embodiment family of thepresent invention will now be described.

Referring to FIGS. 8 a–e, a first baseplate 1400 of a fourth embodimentfamily of the present invention is shown in top (FIG. 8 a), side (FIG. 8b), side cutaway (FIG. 8 c), perspective cutaway (FIG. 8 d) andperspective (FIG. 8 e) views. Also referring to FIGS. 8 f–j, a firsttype 1500 of a second baseplate of the fourth embodiment family is shownin top (FIG. 8 f), side (FIG. 8 g), side cutaway (FIG. 8 h), perspectivecutaway (FIG. 8 i) and perspective (FIG. 8 j) views.

More specifically, the first and second baseplates 1400,1500 are similarto the first and second baseplates of the third embodiment familydescribed above with regard to their outwardly facing surfaces 1402,1502having a convex dome 1403,1503 and a plurality of spikes 1405,1505 asvertebral body contact elements, and the inwardly facing surface 1408 ofthe first baseplate having a perimeter region 1410, all of whichelements in the fourth embodiment family are, for example, identical tothe corresponding elements in the third embodiment family as describedabove. Preferably, the dome 1403,1503 is covered with an osteoconductivelayer of a type known in the art. It should be noted that the convexmesh used in other embodiments of the present invention is suitable foruse with these other vertebral body contact elements, and can beattached over the convex dome 1403,1503 by laser welding, or morepreferably, by plasma burying (where the perimeter region of the convexmesh is buried under a plasma coating, which coating secures to theoutwardly facing surface of the baseplate to which it is applied, andthus secures the convex mesh to the outwardly facing surface).

For example, and referring now to FIGS. 8 aa–8 dd, an alternate firstbaseplate 9400 of the fourth embodiment family is shown in top (FIG. 8aa) and side cutaway (FIG. 8 bb) views, respectively, and an alternatesecond baseplate 9500 of the fourth embodiment family is shown in top(FIG. 8 cc) and side cutaway (FIG. 8 dd) views, respectively. Thealternate first and second baseplates 9400,9500 are similar to the firstand second baseplates of the fourth embodiment family described above,having identical features numbered in the 9400's and 9500's rather thanthe 1400's and 1500's, respectively. However, the alternate baseplatesare different in that each has a convex mesh 9450,9550 attached to theoutwardly facing surface 9402,9502 by burying the perimeter of the mesh9450,9550 in a plasma coating (or other suitable material, preferablyhaving an osteoconductive surface) 9452,9552 that is secured to both theoutwardly facing surface 9402,9502 and the mesh 9450,9550. The plasmacoating 9452,9552 serves not only to secure the mesh 9450,9550, but alsoto facilitate securing of the baseplates to the adjacent vertebralendplates. It should be understood that these alternate baseplates canbe used in place of the other baseplates discussed herein, to constructartificial discs contemplated by the present invention.

Further, as with the first embodiment family, the two baseplates1400,1500 are joined with a ball and socket joint, and therefore each ofthe baseplates 1400,1500 comprises features that, in conjunction withother components described below, form the ball and socket joint. Theball and socket joint includes a solid ball (described below) mounted toprotrude from the inwardly facing surface 1408 of the first baseplate1400, and a curvate socket formed at a peak of a non-flexible convexstructure (described below) that is attached to the inwardly facingsurface 1508 of the second baseplate 1500, within which curvate socketthe ball is capturable for free rotation and angulation therein. Asshown in FIGS. 8 a–d, the mounting for the ball includes a centralinwardly directed post 1412 that extends from the inwardly facingsurface 1408 of the first baseplate 1400, which post's head endcompression locks into a central bore in the ball (described below). Asshown in FIGS. 8 e–h, the second baseplate 1500 includes an inwardlyfacing surface 1508 and a curvate pocket 1512 formed by a centralportion of the inwardly facing surface 1508 concaving outwardly with asemispherical contour (preferably a hemispherical contour). Preferably,as shown, the curvate pocket 1512 is surrounded by a circumferentialwall 1514 and a circumferential recess 1516 that cooperate with theconvex structure to attach the convex structure to the second baseplate1500.

Referring now to FIGS. 8 k–o, a first type 1600 of a ball of the fourthembodiment family is shown in top (FIG. 8 k), side (FIG. 8 l), sidecutaway (FIG. 8 m), perspective cutaway (FIG. 8 n) and perspective (FIG.8 o) views. The ball 1600 is semispherical (preferably greater thanhemispherical as shown) and therefore defines a spherical contour, andhas a central bore 1602 within which the first baseplate's post's headend is securable. The ball 1600 seats in the curvate pocket 1512 of thesecond baseplate 1500 with the spherical contour defined by the ball1600 closely accommodated by the hemispherical contour of the curvatepocket 1512 for free rotation and free angulation of the ball 1600 inthe curvate pocket 1512.

Referring now to FIGS. 8 p–t, a first type 1700 of a convex structure ofthe fourth embodiment family is shown in top (FIG. 8 p), side (FIG. 8q), side cutaway (FIG. 8 r), perspective cutaway (FIG. 8 s) andperspective (FIG. 8 t) views. The convex structure 1700 is shaped tohave a curved taper on its inwardly facing surface 1706 (as opposed tothe frusto-conical shape of the convex structure in the first and secondembodiment families) and includes a central bore 1702 extending from anoutwardly facing surface 1704 of the convex structure 1700 to aninwardly facing surface 1706 of the convex structure 1700, the bore 1702being surrounded by a curvate taper 1708 on the outwardly facing surface1704, and the curvate taper 1708 being surrounded by a circumferentialrecess 1710 and a circumferential wall 1712. The convex structure 1700is securable to the second baseplate 1500 with the circumferentialrecess 1710 of the convex structure 1700 mating with the circumferentialwall 1514 of the second baseplate 1500 and the circumferential wall 1712of the convex structure 1700 mating with the circumferential recess 1516of the second baseplate 1500, so that when the convex structure 1700 isso secured, the curvate taper 1708 of the convex structure 1700 servesas a curvate pocket opposite the curvate pocket 1512 of the secondbaseplate 1500. That is, the curvate pocket 1708 complements thehemispherical contour of the curvate pocket 1512 of the second baseplate1500 to form a semispherical (and preferably greater than hemisphericalas shown) socket 1707 defining a spherical contour that closelyaccommodates the spherical contour defined by the ball 1600 so that theball 1600 is captured in the socket 1707 for free rotation and freeangulation of the ball 1600 therein. (When the formed socket 1707 isgreater than hemispherical, and the shape of the ball 1600 is greaterthan hemispherical, the ball 1600 cannot escape the formed socket 1707.)Further, the inwardly facing surface 1706 of the convex structure 1700has a perimeter region 1714 that faces the perimeter region 1410 of thefirst baseplate 1400 when the convex structure 1700 is secured to thesecond baseplate 1500.

Referring now to FIGS. 8 u–y, an assembled first preferred embodiment ofthe fourth embodiment family is shown in top (FIG. 8 u), side (FIG. 8v), side cutaway (FIG. 8 w), perspective cutaway (FIG. 8 x) andperspective (FIG. 8 y) views. More particularly, assembly of the disc ispreferably as follows. The ball 1600 is seated within the curvate pocket1512 of the second baseplate 1500 (the curvate pocket 1512 has anopening diameter that accommodates the ball 1600) so that the sphericalcontour defined by the ball 1600 is closely accommodated by thehemispherical contour of the curvate pocket 1512. Thereafter, the convexstructure 1700 is secured to the second baseplate 1500 as describedabove with the convex structure's curvate pocket 1708 (the curvatetapered lip 1708 of the convex structure's central bore 1702) fittingagainst the ball 1600 so that the ball 1600 is captured in the socket1707 (formed by the curvate taper 1708 and the curvate pocket 1512) forfree rotation and free angulation of the ball 1600 therein. Thereafter,the first baseplate's post's head end is secured into the bore 1602 ofthe ball 1600. The central bore 1702 of the convex structure 1700 has adiameter that accommodates the diameter of the post 1412, but not thediameter of the ball 1600. Therefore, after the ball 1600 is secured inthe socket 1707, the post 1412 fits through the bore 1702 so that thehead end of the post 1412 can be compression locked to the ball 1600,but the ball 1600 is prevented from escaping the socket 1707 through thecentral bore 1702 of the convex structure 1700.

Accordingly, the ball 1600 is captured in the socket 1707 (so that thedevice will not separate in tension), can freely rotate in the socket1707 about the longitudinal axis of the post 1412, and can freelyangulate in the socket 1707 about a centroid of motion located at thecenter of the sphere defined by the ball 1600. Further, the opening ofthe bore 1702 of the cap 1700 on the inwardly facing surface 1706 of theconvex structure 1700 is large enough to permit the post 1412 toangulate (about the centroid of motion at the center of the spheredefined by the ball 1600) with respect to the bore 1702 as the ball 1600angulates in the socket 1707. Preferably, the conformation of the bore1702 accommodates angulation of the post 1412 at least until theperimeter regions 1410,1714 of the inwardly facing surfaces1408,1508/1706 meet. Further preferably, the perimeter regions 1410,1714have corresponding contours, so that the meeting of the perimeterregions reduces any surface wearing.

Referring now to FIG. 8 z, an assembled alternate first preferredembodiment of the fourth embodiment family is shown in side cutawayview. This alternate first preferred embodiment incorporates amulti-part second baseplate (with first part 15000 a and second part15000 b) housing a spring member 15100 that provides axialcompressibility, such that a compressive load applied to the baseplatesis borne by the spring member 15100. Elements of this alternate firstpreferred embodiment that are also elements found in the first preferredembodiment of the fourth embodiment family are like numbered, and theassembly of this alternate first preferred embodiment is identical tothat of the first preferred embodiment, with some differences due to theincorporation of the spring member 15100. (For example, the secondbaseplate features are numbered in the 15000's rather than the 1500's.)More particularly, assembly of the disc is preferably as follows. Theball 1600 is seated within the curvate pocket 15120 of the inwardlyfacing surface 15090 b to the second baseplate second part 15000 b (thecurvate pocket 15120 has an opening diameter that accommodates the ball1600) so that the spherical contour defined by the ball 1600 is closelyaccommodated by the hemispherical contour of the curvate pocket 15120.The spring member 15100 is then disposed on the outwardly facing surface15020 b of the second baseplate second part 15000 b. While not limitedto any particular structure, assembly, or material, a spring memberproviding shock absorption preferably includes an elastomeric material,such as, for example, polyurethane or silicon, and a spring memberproviding shock dampening preferably includes a plastic material, suchas, for example, polyethylene. It should be understood that metalsprings may alternatively or additionally be used. The illustratedspring member 15100 is formed of an elastomeric material, for example.The illustrated spring member 15100 is ring-shaped, for example, suchthat it fits just inside the circumferential edge of the outwardlyfacing surface 15020 b of the second baseplate second part 15000 b asshown.

The ball 1600, second baseplate second part 15000 b, and spring member15100 are then disposed on the inwardly facing surface 15090 a of thesecond baseplate first part 15000 a, such that the spring member 15100is incarcerated between the inwardly facing surface 15090 a of thesecond baseplate first part 15000 a and the outwardly facing surface15020 b of the second baseplate second part 15000 b. The secondbaseplate second part 15000 b should be dimensioned such that, and thespring member 15100 should have an uncompressed height such that, a gapis present between the outwardly facing surface 15020 b of the secondbaseplate second part 15000 b and the inwardly facing surface 15090 a ofthe second baseplate first part 15000 a when the disc is assembled. Thegap preferably has a height equivalent to the anticipated distance thatthe spring member 15100 will compress under an anticipated load.Thereafter, the convex structure 1700 is secured to the second baseplatefirst part 15000 a, with the convex structure's curvate pocket 1708 (thecurvate tapered lip 1708 of the convex structure's central bore 1702)fitting against the ball 1600 so that the ball 1600 is captured in thesocket 1707 (formed by the curvate taper 1708 and the curvate pocket15120) for free rotation and free angulation of the ball 1600 therein.Although any suitable method is contemplated by the present invention,the convex structure 1700 preferably is secured by compression locking(a laser weld can alternatively or additionally be used, or othersuitable attachment means). The second baseplate first part 15000 a mayalso additionally or alternatively be threaded to the convex structure1700 for increased stability of the attachment. It should be understoodthat the second baseplate second part 15000 b preferably fits looselywithin the convex structure 1700 and the second baseplate first part15000 a, so that when the first baseplate 1400 is compressed toward thesecond baseplate first part 15000 a, the second baseplate second part15000 b may travel toward the second baseplate first part 15000 a as thespring member 15100 compresses. Thereafter, the first baseplate's post'shead end is secured into the bore 1602 of the ball 1600. The centralbore 1702 of the convex structure 1700 has a diameter that accommodatesthe diameter of the post 1412, but not the diameter of the ball 1600.Therefore, after the ball 1600 is secured in the socket 1707, the post1412 fits through the bore 1702 so that the head end of the post 1412can be compression locked to the ball 1600, but the ball 1600 isprevented from escaping the socket 1707 through the central bore 1702 ofthe convex structure 1700.

Accordingly, the ball 1600 is captured in the socket 1707 (so that thedevice will not separate in tension), can freely rotate in the socket1707 about the longitudinal axis of the post 1412, and can freelyangulate in the socket 1707 about a centroid of motion located at thecenter of the sphere defined by the ball 1600. Further, the opening ofthe bore 1702 of the convex structure 1700 on the inwardly facingsurface 1706 of the convex structure 1700 is large enough to permit thepost 1412 to angulate (about the centroid of motion at the center of thesphere defined by the ball 1600) with respect to the bore 1702 as theball 1600 angulates in the socket 1707. Preferably, the conformation ofthe bore 1702 accommodates angulation of the post 1412 at least untilthe perimeter regions 1410,1714 of the inwardly facing surfaces1408,15080/1706 meet. Further preferably, the perimeter regions1410,1714 have corresponding contours, so that the meeting of theperimeter regions reduces any surface wearing. Further accordingly, inthis alternate first preferred embodiment, part or all of a compressiveload applied to the baseplates will be borne by the spring member 15100,which will dampen the load and/or absorb the load and preferably helpreturn the baseplates to their original uncompressed relative positions.

Accordingly, when a device of the first preferred embodiment of thefourth embodiment family is assembled, the baseplates 1400,1500 (or1400,15000 a) are rotatable relative to one another because the ball1600 rotates freely within the socket 1707, and angulatable relative toone another because the ball 1600 angulates freely within the socket1707. Because the ball 1600 is held within the socket 1707 by thesecuring of the tail end of the central post 1412 of the first baseplate1400 to the ball 1600 and the securing of the convex structure 1700 tothe second baseplate 1500 (or second baseplate first part 15000 a), theartificial disc can withstand tension loading of the baseplates1400,1500 (or 1400,15000 a). More particularly, when a tension load isapplied to the baseplates 1400,1500 (or 1400,15000 a) the ball 1600seeks to pass through the bore 1702 in the convex structure 1700.However, the curvate taper 1708 of the bore 1702 prevents the ball 1600from exiting the socket 1707. Therefore, the assembly does not comeapart under normally experienced tension loads. This ensures that noindividual parts of the assembly will pop out or slip out from betweenthe vertebral bodies when, e.g., the patient stretches or hangs whileexercising or performing other activities. Thus, in combination with thesecuring of the baseplates 1400,1500 (or 1400,15000 a) to the adjacentvertebral bones via the domes 1403,1503 (or 1403,15030) and spikes1405,1505 (or 1405,15050), the disc assembly has an integrity similar tothe tension-bearing integrity of a healthy natural intervertebral disc.Also, because the ball 1600 is laterally captured in the socket 1707,lateral translation of the baseplates 1400,1500 (or 1400,15000 a)relative to one another is prevented during rotation and angulation,similar to the performance of healthy natural intervertebral disc.Because the baseplates 1400,1500 (or 1400,15000 a) are made angulatablerelative to one another by the ball 1600 being rotatably and angulatablycoupled in the socket 1707, the disc assembly provides a centroid ofmotion within the sphere defined by the ball 1600. Accordingly, thecentroid of motion of the disc assembly remains centrally locatedbetween the vertebral bodies, similar to the centroid of motion in ahealthy natural intervertebral disc.

The remaining embodiments in the fourth embodiment family of the presentinvention limit the rotation (but preferably not the angulation) of theball in the socket formed by the curvate taper of the convex structureand the hemispherical contour of the curvate pocket of the secondbaseplate. Each embodiment accomplishes this in a different manner, buteach embodiment utilizes interference between a protrusion and a recessto limit the rotation, similar to the manner in which such interferenceis utilized in the third embodiment family. In some embodiments, theprotrusion is preferably hemispherical, and the recess preferably has asemicylindrical contour within which the protrusion fits. In otherembodiments, the protrusion is preferably hemispherical, and the recesspreferably has a curvate contour that is not semicylindrical. (It shouldbe understood that the described formations of the recess and theprotrusion are merely preferred, and that alternate formations, curvateor otherwise, for each are contemplated by the present invention; aparticular shape or location of recess or a particular shape or locationof protrusion is not required; any shape can be used so long as therecess and protrusion interact as desired. For example, the recess inthe second preferred embodiment of the fourth embodiment family has acurvate contour that is not semicylindrical, and the recess in the fifthpreferred embodiment of the fourth embodiment family has a differentcurvate contour that is not semicylindrical, each being formed so thatit optimally interacts with the protrusion in its respectiveembodiment.) The boundaries of the recess define the limits of rotationof the ball within the socket, by allowing movement of the protrusionrelative to the recess as the ball rotates through a certain range inthe socket, but providing interference with the protrusion to preventrotation of the ball beyond that range in the socket. Preferably, forexample, the recess has a depth equivalent to the radius of thehemispherical protrusion, but a radius of curvature greater than that ofthe protrusion. At the same time, the boundaries of the recesspreferably do not limit the angulation of the ball within the socket, atleast until the perimeter regions of the inwardly facing surface of theconvex structure and the inwardly facing surface of the first baseplatemeet. Preferably, for example, the recess has a length greater than therange of movement of the protrusion relative to the recess as the ballangulates in the socket.

Therefore, when assembled, the discs of the remaining preferredembodiments of the fourth embodiment family enable angulation andlimited rotation of the baseplates relative to one another about acentroid of motion that remains centrally located between the baseplates(at the center of the sphere defined by the ball), similar to thecentroid of motion in a healthy natural intervertebral disc that islimited in its rotation by surrounding body structures. A benefit oflimiting the relative rotation of the baseplates is that relativerotation beyond a certain range in a healthy natural disc is neitherneeded nor desired, because, for example, excess strain can be placed onthe facet joints or ligaments thereby. As described with the firstpreferred embodiment of the fourth embodiment family, the constructionalso prevents translation and separation of the baseplates relative toone another during rotation and angulation.

As noted above, each of the remaining preferred embodiments in thisfourth embodiment family forms the protrusion and corresponding recessin a different manner, utilizing components that are either identical orsimilar to the components of the first preferred embodiment, and someembodiments utilize additional components. Each of the remainingpreferred embodiments will now be described in greater detail.

In the second preferred embodiment of the fourth embodiment family ofthe present invention, a hemispherical protrusion is formed on the ball,and interacts in the above-described manner with a recess formedadjacent the socket formed by the curvate taper of the convex structureand the hemispherical contour of the curvate pocket of the secondbaseplate. More particularly, this second preferred embodiment uses thesame first baseplate 1400 as the first preferred embodiment of thefourth embodiment family described above. Referring to FIGS. 9 a–e, asecond type 1800 of second baseplate of the fourth embodiment family isshown in to top (FIG. 9 a), side (FIG. 9 b), side cutaway (FIG. 9 c),perspective cutaway (FIG. 9 d) and perspective (FIG. 9 e) views. Thissecond type 1800 of second baseplate is identical to the first type 1500of second baseplate described above (and thus similar features arereference numbered similar to those of the first type 1500 of secondbaseplate, but in the 1800s rather than the 1500s), except that thissecond type 1800 of second baseplate has a curvate recess 1818 adjacentthe curvate pocket 1812, and preferably in the circumferential wall1814.

As shown in FIGS. 9 a to 9 e, second baseplate 1800 is similarlyconstructed to second base 1500 and includes an outwardly-facing surface1802 having a convex dome 1803 and a plurality of spikes 1805. Theconvex dome 1803 may have similar attributes and be attached to secondbaseplate 1800 similarly to convex dome 1503. Second baseplate 1800 alsoincludes an inwardly-facing surface 1808 and a curvate pocket 1812formed by a central portin of the inwardly-facing surface 1808 concavingoutwardly with a semispherical contour. Preferably, as shown, thecurvate pocket 1812 is surrounded by a circumferential wall 1814 and acircumferential recess 1816 which are similar to circumferential wall1512 and circumferential recess 1516. Further, the second baseplate 1200includes an access hole 1809.

Referring now to FIGS. 9 f–j, a second type 1900 of ball of the fourthembodiment family is shown in top (FIG. 9 f), side (FIG. 9 g), sidecutaway (FIG. 9 h), perspective cutaway (FIG. 9 i) and perspective (FIG.9 j) views. The ball 1900 is identical to the first type 1600 of balldescribed above (and thus similar features are reference numberedsimilar to those of the first type 1600 of ball, but in the 1900s ratherthan the 1600s), except that the semispherical contour of this secondtype 1900 of ball is also interrupted by a hemispherical protrusion1904.

Referring now to FIGS. 9 k–o, a second type 2000 of convex structure ofthe fourth embodiment family is shown in top (FIG. 9 k), side (FIG. 9l), side cutaway (FIG. 9 m), perspective cutaway (FIG. 9 n) andperspective (FIG. 9 o) views. This second type 2000 of convex structureis identical to the first type 1700 of convex structure described above(and thus similar features are reference numbered similar to those ofthe first type 1700 of convex structure, but in the 2000s rather thanthe 1700s), except that this second type 2000 of convex structure has acurvate recess 2016 adjacent the curvate taper 2008.

As shown in the FIGS. 9 k to 9 o, convex structure 2000 is designedsimilarly as convex structure 1700. Convex structure 2000 is shaped tohave a curved taper on its inwardly-facing surface 2006 and includes acentral bore 2002 extending from an outwardly-facing surface 2004 of theconvex structure 2000 to an inwardly-facing surface 2006 of the convexstructure 2000. The bore 2002 is surrounded by a curvet taper 2008 onthe outwardly-facing surface 2004 with the curvet taper 2008 beingsurrounded by a circumferential recess 2010 and a circumferential wall2012. The convex structure 2000 also includes a perimeter region 2014extending radially around the structure.

Referring now to FIGS. 9 p–t, an assembled second preferred embodimentof the fourth embodiment family is shown in top (FIG. 9 p), side (FIG. 9q), side cutaway (FIG. 9 r), perspective cutaway (FIG. 9 s) andperspective (FIG. 9 t) views. It can be seen that the curvate recesses1818,2016 together form the recess described above in the discussion ofthe manner in which these remaining embodiments limit rotation of theball in the socket formed by the curvate taper of the convex structureand the hemispherical contour of the curvate pocket of the secondbaseplate, and that the protrusion 1904 serves as the protrusiondescribed above in the same discussion. Thus, the protrusion 1904 andrecesses 1818,2016 interact in the above described manner to limit therotation of the ball 1900 in the socket 2007. Assembly of the disc isidentical to that of the first preferred embodiment of the fourthembodiment family, except that the protrusion 1904 is longitudinallyaligned with the recess 1818, and the recess 2016 is similarly aligned,so that when the convex structure 2000 is secured to the secondbaseplate 1800, the protrusion 1904 is fitted within the recesses1818,2016 for interaction as described above as the ball 1900 rotatesand angulates in the socket 2007.

Referring now to FIG. 9 u, an assembled alternate second preferredembodiment of the fourth embodiment family is shown in side cutawayview. This alternate second preferred embodiment incorporates amulti-part second baseplate (with first part 18000 a and second part18000 b) housing a spring member 18100 that provides axialcompressibility, such that a compressive load applied to the baseplatesis borne by the spring member 18100. Elements of this alternate secondpreferred embodiment that are also elements found in the secondpreferred embodiment of the fourth embodiment family are like numbered.(The second baseplate features are numbered in the 18000's rather thanthe 1800's.) The curvate recesses 18180,2016 together form the recessdescribed above, and the protrusion 1904 serves as the protrusiondescribed above, and thus the protrusion 1904 and recesses 18180,2016interact in the above described manner to limit the rotation of the ball1900 in the socket 2007.

Assembly of this alternate second preferred embodiment is identical tothat of the first preferred embodiment of the fourth embodiment family,except that the protrusion 1904 is longitudinally aligned with therecess 18180, and the recess 2016 is similarly aligned, so that when theconvex structure 2000 is secured to the second baseplate first part18000 a, the protrusion 1904 is fitted within the recesses 18180,2016for interaction as described above as the ball 1900 rotates andangulates in the socket 2007. It should be understood that the secondbaseplate second part 18000 b preferably fits loosely within the convexstructure 2000 and the second baseplate first part 18000 a, so that whenthe first baseplate 1400 is compressed toward the second baseplate firstpart 18000 a, the second baseplate second part 18000 b may travel towardthe second baseplate first part 18000 a as the spring member 18100compresses. While not limited to any particular structure, assembly, ormaterial, a spring member providing shock absorption preferably includesan elastomeric material, such as, for example, polyurethane or silicon,and a spring member providing shock dampening preferably includes aplastic material, such as, for example, polyethylene. It should beunderstood that metal springs may alternatively or additionally be used.The illustrated spring member 18100 is formed of an elastomericmaterial, for example. The illustrated spring member 18100 isring-shaped, for example, such that it fits just inside thecircumferential edge of the outwardly facing surface 18020 b of thesecond baseplate second part 18000 b as shown. The second baseplatesecond part 18000 b should be dimensioned such that, and the springmember 18100 should have an uncompressed height such that, a gap ispresent between the outwardly facing surface 18020 b of the secondbaseplate second part 18000 b and the inwardly facing surface 18090 a ofthe second baseplate first part 18000 a when the disc is assembled. Thegap preferably has a height equivalent to the anticipated distance thatthe spring member 18100 will compress under an anticipated load.Accordingly, in this alternate second preferred embodiment, part or allof a compressive load applied to the baseplates will be borne by thespring member 18100, which will dampen the load and/or absorb the loadand preferably help return the baseplates to their original uncompressedrelative positions.

In the third preferred embodiment of the fourth embodiment family of thepresent invention, a hemispherical protrusion is formed to protrude intothe socket formed by the curvate taper of the convex structure and thehemispherical contour of the curvate pocket of the second baseplate, andinteracts in the above-described manner with a semicylindrical recessformed on the ball. More particularly, this third preferred embodimentuses the same first baseplate 1400 as the first preferred embodiment ofthe fourth embodiment family described above. Referring to FIGS. 10 a–e,a third type 2100 of second baseplate of the fourth embodiment family isshown in top (FIG. 10 a), side (FIG. 10 b), side cutaway (FIG. 10 c),perspective cutaway (FIG. 10 d) and perspective (FIG. 10 e) views. Thisthird type 2100 of second baseplate is identical to the first type 1500of second baseplate described above (and thus similar features arereference numbered similar to those of the first type 1500 of secondbaseplate, but in the 2100s rather than the 1500s), except that thisthird type 2100 of second baseplate has a recess 2118 adjacent thecurvate pocket 2112, and preferably in the circumferential wall 2114 asshown.

As shown in FIG. 10 a to 10 e, second baseplate 2100 is similarlydesigned as second baseplate 1500 and includes an outwardly-facingsurface 2102 having a convex dome 2103 and a plurality of spikes 2105that may act as vertebral body contact elements. The second baseplate2100 also includes an inwardly-facing surface 2108 and a curvate pocket2112 formed by a central portion of the inwardly-facing surface 2108concaving outwardly with the semispherical contour. Preferably, asshown, the curvet pocket 2112 is surrounded by a circumferential wall2114 and a circumferential recess 2116 that operates similarly to thecircumferential wall and circumferential recess 1514 and 1516,respectively.

Referring now to FIGS. 10 f–j, a third type 2200 of ball of the fourthembodiment family is shown in top (FIG. 10 f), side (FIG. 10 g), sidecutaway (FIG. 10 h), perspective cutaway (FIG. 10 i) and perspective(FIG. 10 j) views. The ball 2200 is identical to the first type 1600 ofball described above and includes central bore 2202 (and thus similarfeatures are reference numbered similar to those of the first type 1600of ball, but in the 2200s rather than the 1600s), except that thesemispherical contour of this third type 2200 of ball is alsointerrupted by a curvate recess 2204.

Referring now to FIGS. 10 k–o, a third type 2300 of convex structure ofthe fourth embodiment family is shown in top (FIG. 10 k), side (FIG. 10l), side cutaway (FIG. 10 m), perspective cutaway (FIG. 10 n) andperspective (FIG. 10 o) views. This third type 2300 of convex structureis identical to the first type 1700 of convex structure described above(and thus similar features are reference numbered similar to those ofthe first type 1700 of convex structure, but in the 2300s rather thanthe 1700s), except that this third type 2300 of convex structure has aprotrusion 2316 adjacent the curvate taper 2008.

As shown in FIGS. 10 k to 10 o, the convex structure 2300 is similarlydesigned to convex structure 1700 and includes an inwardly-facingsurface 2306 and a central bore 2302 extending from an outwardly-facingsurface 2304 of the convex structure. The bore 1702 is surrounded by acurvet taper 2308 on the outwardly-facing surface 2304 and the curvatetaper 2308 is surrounded by a circumferential recess 2310 and acircumferential wall 2312. Further, the inwardly-facing surface 2306 ofthe convex structure 2300 has a perimeter region 2314 that faces theperimeter region 1410 of the first baseplate 1400 when the convexstructure is secured to the second baseplate 2100.

Referring now to FIGS. 10 p–t, an assembled third preferred embodimentof the fourth embodiment family is shown in top (FIG. 10 p), side (FIG.10 q), side cutaway (FIG. 10 r), perspective cutaway (FIG. 10 s) andperspective (FIG. 10 t) views. It can be seen that the curvate recess2204 of the ball 2200 forms the recess described above in the discussionof the manner in which these remaining embodiments limit rotation of theball in the socket formed by the curvate taper of the convex structureand the hemispherical contour of the curvate pocket of the secondbaseplate, and that the protrusion 2316 fits into the recess 2118 toserve as the protrusion described above in the same discussion. Thus,the protrusion 2316 and the recess 2204 interact in the above describedmanner to limit the rotation of the ball 2200 in the socket 2307.Assembly of the disc is identical to that of the first preferredembodiment of the fourth embodiment family, except that the protrusion2316 is longitudinally aligned with the recess 2204 and the recess 2118during assembly so that the protrusion 2316 fits into the recess 2118 toextend into the recess 2204 for interaction as described above as theball 2200 rotates and angulates in the socket 2307.

Referring now to FIG. 10 u, an assembled alternate third preferredembodiment of the fourth embodiment family is shown in side cutawayview. This alternate third preferred embodiment incorporates amulti-part second baseplate (with first part 21000 a and second part21000 b) housing a spring member 21100 that provides axialcompressibility, such that a compressive load applied to the baseplatesis borne by the spring member 21100. Elements of this alternate thirdpreferred embodiment that are also elements found in the third preferredembodiment of the fourth embodiment family are like numbered. (Thesecond baseplate features are numbered in the 21000's rather than the2100's.) The curvate recess 2204 of the ball 2200 forms the recessdescribed above, and the protrusion 2316 fits into the recess 21180 toserve as the protrusion described above, and thus, the protrusion 2316and the recess 2204 interact in the above described manner to limit therotation of the ball 2200 in the socket 2307.

Assembly of this alternate third preferred embodiment is identical tothat of the first preferred embodiment of the fourth embodiment family,except that the protrusion 2316 is longitudinally aligned with therecess 2204 and the recess 21180 during assembly so that the protrusion2316 fits into the recess 21180 to extend into the recess 2204 forinteraction as described above as the ball 2200 rotates and angulates inthe socket 2307. It should be understood that the second baseplatesecond part 21000 b preferably fits loosely within the convex structure2300 and the second baseplate first part 21000 a, so that when the firstbaseplate 1400 is compressed toward the second baseplate first part21000 a, the second baseplate second part 21000 b may travel toward thesecond baseplate first part 21000 a as the spring member 21100compresses. While not limited to any particular structure, assembly, ormaterial, a spring member providing shock absorption preferably includesan elastomeric material, such as, for example, polyurethane or silicon,and a spring member providing shock dampening preferably includes aplastic material, such as, for example, polyethylene. It should beunderstood that metal springs may alternatively or additionally be used.The illustrated spring member 21100 is formed of an elastomericmaterial, for example. The illustrated spring member 21100 isring-shaped, for example, such that it fits just inside thecircumferential edge of the outwardly facing surface 21020 b of thesecond baseplate second part 21000 b as shown. The second baseplatesecond part 21000 b should be dimensioned such that, and the springmember 21100 should have an uncompressed height such that, a gap ispresent between the outwardly facing surface 21020 b of the secondbaseplate second part 21000 b and the inwardly facing surface 21090 a ofthe second baseplate first part 21000 a when the disc is assembled. Thegap preferably has a height equivalent to the anticipated distance thatthe spring member 21100 will compress under an anticipated load.Accordingly, in this alternate third preferred embodiment, part or allof a compressive load applied to the baseplates will be borne by thespring member 21100, which will dampen the load and/or absorb the loadand preferably help return the baseplates to their original uncompressedrelative positions.

In the fourth preferred embodiment of the fourth embodiment family ofthe present invention, a pin is secured in a pin hole so that thehemispherical head of the pin protrudes into the socket formed by thecurvate taper of the convex structure and the hemispherical contour ofthe curvate pocket of the second baseplate, and interacts in theabove-described manner with a semicylindrical recess formed on the ball.More particularly, this fourth preferred embodiment uses the same firstbaseplate 1400 of the first preferred embodiment, and the same ball 2200and second baseplate 2100 of the fourth preferred embodiment. Referringto FIGS. 11 a–e, a fourth type 2400 of convex structure of the fourthembodiment family is shown in top (FIG. 11 a), side (FIG. 11 b), sidecutaway (FIG. 11 c), perspective cutaway (FIG. 11 d) and perspective(FIG. 11 e) views. This fourth type 2400 of convex structure isidentical to the first type 1700 of convex structure described above(and thus similar features are reference numbered similar to those ofthe first type 1700 of convex structure, but in the 2400s rather thanthe 1700s), except that this fourth type 2400 of convex structure has alateral through hole (e.g., a pin hole 2416) and a protrusion (e.g., apin 2418) secured in the pin hole 2416 (as shown in FIGS. 11 f–j) andjutting into the socket 2407.

As shown in FIG. 11 a to 11 e, convex structure 2400 is similarlydesigned to convex structure 1700 and includes an inwardly facingsurface 2406 and a central bore 2402 extending from an outwardly-facingsurface 2404 of the convex structure 2400 to an inwardly-facing 2406 ofthe convex structure. The bore 2402 is surrounded by a curvate taper2408 on the outwardly-facing surface 2404 and the curvate taper issurrounded by a circumferential recess 2410 and a circumferential wall2412. Further, the inwardly-facing surface 2406 of the convex structure2400 has a perimeter region 2414. Convex structure 2400 also includes apinhole 2416 that is not included in the embodiment of convex structure1700.

Referring now to FIGS. 11 f–j, an assembled fourth preferred embodimentof the fourth embodiment family is shown in top (FIG. 11 f), side (FIG.11 g), side cutaway (FIG. 11 h), perspective cutaway (FIG. 11 i) andperspective (FIG. 11 j) views. It can be seen that the curvate recess2204 of the ball 2200 forms the recess described above in the discussionof the manner in which these remaining embodiments limit rotation of theball in the socket formed by the curvate taper of the convex structureand the hemispherical contour of the curvate pocket of the secondbaseplate, and that the head of the pin 2418 serves as the protrusiondescribed above in the same discussion. Thus, the head of the pin 2418and the recess 2204 interact in the above described manner to limit therotation of the ball 2200 in the socket 2407. Assembly of the disc isidentical to that of the first preferred embodiment of the fourthembodiment family, except that the head of the pin 2418 islongitudinally aligned with the recess 2204 and the recess 2118 duringassembly so that the head of the pin 2418 fits into the recess 2118 toextend into the recess 2204 for interaction as described above as theball 2200 rotates and angulates in the socket 2407.

Referring now to FIG. 11 k, an assembled alternate fourth preferredembodiment of the fourth embodiment family is shown in side cutawayview. This alternate fourth preferred embodiment incorporates amulti-part second baseplate (with first part 21000 a and second part21000 b) housing a spring member 21100 that provides axialcompressibility, such that a compressive load applied to the baseplatesis borne by the spring member 21100. Elements of this alternate fourthpreferred embodiment that are also elements found in the fourthpreferred embodiment of the fourth embodiment family are like numbered.(The second baseplate features are numbered in the 21000's rather thanthe 2100's.) The curvate recess 2204 of the ball 2200 forms the recessdescribed above, and the head of the pin 2418 serves as the protrusiondescribed above, and thus, the head of the pin 2418 and the recess 2204interact in the above described manner to limit the rotation of the ball2200 in the socket 2407.

Assembly of this alternate fourth preferred embodiment is identical tothat of the first preferred embodiment of the fourth embodiment family,except that the head of the pin 2418 is longitudinally aligned with therecess 2204 and the recess 21180 during assembly so that the head of thepin 2418 fits into the recess 21180 to extend into the recess 2204 forinteraction as described above as the ball 2200 rotates and angulates inthe socket 2407. It should be understood that the second baseplatesecond part 21000 b preferably fits loosely within the convex structure2400 and the second baseplate first part 21000 a, so that when the firstbaseplate 1400 is compressed toward the second baseplate first part21000 a, the second baseplate second part 21000 b may travel toward thesecond baseplate first part 21000 a as the spring member 21100compresses. While not limited to any particular structure, assembly, ormaterial, a spring member providing shock absorption preferably includesan elastomeric material, such as, for example, polyurethane or silicon,and a spring member providing shock dampening preferably includes aplastic material, such as, for example, polyethylene. It should beunderstood that metal springs may alternatively or additionally be used.The illustrated spring member 21100 is formed of an elastomericmaterial, for example. The illustrated spring member 21100 isring-shaped, for example, such that it fits just inside thecircumferential edge of the outwardly facing surface 21020 b of thesecond baseplate second part 21000 b as shown. The second baseplatesecond part 21000 b should be dimensioned such that, and the springmember 21100 should have an uncompressed height such that, a gap ispresent between the outwardly facing surface 21020 b of the secondbaseplate second part 21000 b and the inwardly facing surface 21090 a ofthe second baseplate first part 21000 a when the disc is assembled. Thegap preferably has a height equivalent to the anticipated distance thatthe spring member 21100 will compress under an anticipated load.Accordingly, in this alternate first preferred embodiment, part or allof a compressive load applied to the baseplates will be borne by thespring member 21100, which will dampen the load and/or absorb the loadand preferably help return the baseplates to their original uncompressedrelative positions.

In the fifth preferred embodiment of the fourth embodiment family of thepresent invention, a ball bearing protrudes into the socket formed bythe curvate taper of the convex structure and the hemispherical contourof the curvate pocket of the second baseplate, and interacts in theabove-described manner with a recess formed on the ball. Moreparticularly, this fifth preferred embodiment uses the same firstbaseplate 1400 of the first preferred embodiment, and the same secondbaseplate 2100 of the third preferred embodiment. Referring to FIGS. 12a–e, a fifth type 2500 of convex structure of the fourth embodimentfamily is shown in top (FIG. 12 a), side (FIG. 12 b), side cutaway (FIG.12 c), perspective cutaway (FIG. 12 d) and perspective (FIG. 12 e)views. This fifth type 2500 of convex structure is identical to thefirst type 1700 of convex structure described above (and thus similarfeatures are reference numbered similar to those of the first type 1700of convex structure, but in the 2500s rather than the 1700s), exceptthat this fifth type 2500 of convex structure has a has a recess 2516adjacent the curvate taper 2508.

As shown in FIGS. 11 a to 11 e, convex structure 2500 is similarlydesigned to convex structure 1700 and includes an inwardly facingsurface 2406 and a central bore 2502 extending from an outwardly-facingsurface 2504 of the convex structure 2500 to an inwardly-facing surface2506 of the convex structure. The bore 2502 is surrounded by a curvatetaper 2408 on the outwardly-facing surface 2504 and the curvate taper issurrounded by a circumferential recess 2510 and a circumferential wall2512. Further, the inwardly-facing surface 2506 of the convex structure2500 has a perimeter region 2514.

Referring to FIGS. 12 f–j, a fourth type of ball 2700 of the fourthembodiment family is shown in top (FIG. 12 f), side (FIG. 12 g), sidecutaway (FIG. 12 h), perspective cutaway (FIG. 12 i) and perspective(FIG. 12 j) views. The ball 2700 is identical to the first type 1600 ofball described above and includes a central bore 2702, (and thus similarfeatures are reference numbered similar to those of the first type 1600of ball, but in the 2700s rather than the 1600s), except that thesemispherical contour of this third type 2700 of ball is alsointerrupted by a curvate recess 2704.

Referring now to FIGS. 12 k–o, an assembled fifth preferred embodimentof the fourth embodiment family is shown in top (FIG. 12 k), side (FIG.12 l), side cutaway (FIG. 12 m), perspective cutaway (FIG. 12 n) andperspective (FIG. 120) views. A ball bearing 2600 of the fourthembodiment family is captured for free rotation and angulation, with onepart of the ball bearing 2600 closely accommodated in the recesses2118,2516, and another part of the ball bearing 2600 protruding into thesocket to interact with the curvate recess 2704 of the ball 2700. It canbe seen that the curvate recess 2704 of the ball 2700 forms the recessdescribed above in the discussion of the manner in which these remainingembodiments limit rotation of the ball in the socket, and that the ballbearing 2600 serves as the protrusion described above in the samediscussion. Thus, the ball bearing 2600 and the recess 2704 interact inthe above described manner to limit the rotation of the ball 2700 in thesocket 2507. Assembly of the disc is identical to that of the firstpreferred embodiment of the fourth embodiment family, except that therecess 2704 is aligned with the curvate recess 2118 during assembly sothat the ball bearing 2600 can be and is then placed into the recesses2118,2704 (and then captured in the recess 2118 by the recess 2516 ofthe convex structure 2500) for interaction as described above as theball 2700 rotates and angulates in the socket 2507.

Referring now to FIG. 12 p, an assembled alternate fifth preferredembodiment of the fourth embodiment family is shown in side cutawayview. This alternate fifth preferred embodiment incorporates amulti-part second baseplate (with first part 21000 a and second part21000 b) housing a spring member 21100 that provides axialcompressibility, such that a compressive load applied to the baseplatesis borne by the spring member 21100. Elements of this alternate fifthpreferred embodiment that are also elements found in the fifth preferredembodiment of the fourth embodiment family are like numbered. (Thesecond baseplate features are numbered in the 21000's rather than the2100's.) The curvate recess 2704 of the ball 2700 forms the recessdescribed above, and the ball bearing 2600 serves as the protrusiondescribed above, and thus, the ball bearing 2600 and the recess 2704interact in the above described manner to limit the rotation of the ball2700 in the socket 2507.

Assembly of this alternate fifth preferred embodiment is identical tothat of the first preferred embodiment of the fourth embodiment family,except that the recess 2704 is aligned with the curvate recess 21180during assembly so that the ball bearing 2600 can be and is then placedinto the recesses 21180,2704 (and then captured in the recess 21180 bythe recess 2516 of the convex structure 2500) for interaction asdescribed above as the ball 2700 rotates and angulates in the socket2507. It should be understood that the second baseplate second part21000 b preferably fits loosely within the convex structure 2500 and thesecond baseplate first part 21000 a, so that when the first baseplate1400 is compressed toward the second baseplate first part 21000 a, thesecond baseplate second part 21000 b may travel toward the secondbaseplate first part 21000 a as the spring member 21100 compresses.While not limited to any particular structure, assembly, or material, aspring member providing shock absorption preferably includes anelastomeric material, such as, for example, polyurethane or silicon, anda spring member providing shock dampening preferably includes a plasticmaterial, such as, for example, polyethylene. It should be understoodthat metal springs may alternatively or additionally be used. Theillustrated spring member 21100 is formed of an elastomeric material,for example. The illustrated spring member 21100 is ring-shaped, forexample, such that it fits just inside the circumferential edge of theoutwardly facing surface 21020 b of the second baseplate second part21000 b as shown. The second baseplate second part 21000 b should bedimensioned such that, and the spring member 21100 should have anuncompressed height such that, a gap is present between the outwardlyfacing surface 21020 b of the second baseplate second part 21000 b andthe inwardly facing surface 21090 a of the second baseplate first part21000 a when the disc is assembled. The gap preferably has a heightequivalent to the anticipated distance that the spring member 21100 willcompress under an anticipated load. Accordingly, in this alternate firstpreferred embodiment, part or all of a compressive load applied to thebaseplates will be borne by the spring member 21100, which will dampenthe load and/or absorb the load and preferably help return thebaseplates to their original uncompressed relative positions.

While there has been described and illustrated specific embodiments ofan artificial disc, it will be apparent to those skilled in the art thatvariations and modifications are possible without deviating from thebroad spirit and principle of the invention. The invention, therefore,shall not be limited to the specific embodiments discussed herein.

1. An intervertebral spacer device, comprising: a first baseplate,having an outwardly facing surface and an inwardly facing surface, theinwardly facing surface having a central hole; a second baseplate,having an outwardly facing surface and an integrated convex structure,the convex structure including a curvate pocket, the convex structure'scurvate pocket being formed by a central portion of an outwardly facingsurface of the convex structure concaving inwardly to define asemispherical contour, the convex structure's curvate pocket furtherhaving an apex at a center of the convex structure's curvate pocket'ssemispherical contour, the convex structure further having a borethrough the convex structure's curvate pocket's apex from the convexstructure's outwardly facing surface to the convex structure's inwardlyfacing surface, the second baseplate having on its outwardly facingsurface an access hole leading to the convex structure's curvate pocket;a post having a longitudinal axis, a tail end, and a head end having aball defining a spherical contour; a cap having a first part and asecond part, the first part having an inwardly facing surface and acurvate pocket having a semispherical contour, the cap's curvate pocketbeing formed by a central portion of the cap's inwardly facing surfaceconcaving outwardly; and a spring member; wherein the tail end isdisposable through the access hole and through the bore, and the headend is disposable through the access hole and prevented from passagethrough the bore, such that the ball is seatable in the convexstructure's curvate pocket; and wherein the tail end is securable in thecentral hole; and wherein the first part of the cap is disposed suchthat the cap's curvate pocket's semispherical contour opposes the convexstructure's curvate pocket's semispherical contour such that thesemispherical contours together define a curvate socket defining aspherical contour that closely accommodates the ball's spherical contourfor rotation and angulation of the ball in the curvate socket about acentral portion of the ball, and such that the post is accommodated forrotation in the bore about the longitudinal axis as the ball rotates inthe curvate socket, and such that the post is accommodated forangulation in the bore about the ball's central portion as the ballangulates in the curvate socket; and wherein the spring member isdisposed between the first part of the cap and the second part of thecap, and the second part of the cap is securable to the secondbaseplate, such that a compressive load applied to the outwardly facingsurfaces of the baseplates is borne by the spring member.
 2. Theintervertebral spacer device of claim 1, wherein each of the inwardlyfacing surface of the first baseplate and the inwardly facing surface ofthe convex structure has a respective perimeter region, and theperimeter regions have corresponding contours that reduce surfacewearing during rotation and angulation of the ball in the curvatesocket.
 3. The intervertebral spacer device of claim 1, wherein theaccess hole is surrounded by a circular recess, and the second part ofthe cap is securable in the circular recess.
 4. The intervertebralspacer device of claim 1, wherein the second part of the cap iscompression lockable to the second baseplate.
 5. The intervertebralspacer device of claim 1, wherein the bore is tapered to a largerdiameter toward the convex structure's inwardly facing surface, and thepost is accommodated, by the bore being tapered, for angulation in thebore about the ball's central portion as the ball angulates in thecurvate socket.
 6. The intervertebral spacer device of claim 1, whereinat least one of the curvate pockets has a hemispherical contour.
 7. Theintervertebral spacer device of claim 1, wherein the second part of thecap has an outwardly facing surface and at least one of the second partof the cap and the first baseplate includes an osteoinductive vertebralbody contact surface on its outwardly facing surface.
 8. Theintervertebral spacer device of claim 1, wherein the tail end iscompression lockable into the central hole.
 9. An intervertebral spacerdevice, comprising: a first baseplate, having an outwardly facingsurface and an inwardly facing surface, the inwardly facing surfacehaving a central post secured thereto, the post having a longitudinalaxis and a ball at a head end of the post that is inwardly directedtoward the second baseplate, the ball defining a spherical contour; asecond baseplate, having an outwardly facing surface and an inwardlyfacing surface, the second baseplate including a convex structureintegral therewith and a cap secured thereto, the convex structure andthe cap together establishing a curvate socket communicating with acentral bore through the convex structure, the curvate socket defining aspherical contour; wherein the ball is capturable in the curvate socket,with the curvate socket's spherical contour accommodating the ball'sspherical contour for rotation and angulation of the ball in the curvatesocket about a central portion of the ball; and with the central boreaccommodating the post for rotation in the central bore about thelongitudinal axis as the ball rotates in the curvate socket, andaccommodating the post for angulation in the central bore about theball's central portion as the ball angulates in the curvate socket; andfurther comprising a spring member housed by the cap such that acompressive load applied to the outwardly facing surfaces of thebaseplates is borne by the spring member.
 10. The intervertebral spacerdevice of claim 9, wherein each of the convex structure and the cap hasa respective curvate pocket, the second baseplate has an access holeleading to the convex structure's curvate pocket and accommodatingpassage of the post and the ball for seating of the ball in the convexstructure's curvate pocket with the post disposed in the central bore,and the cap is secured to the second baseplate such that the curvatepockets of the convex structure and the cap oppose one another to definethe curvate socket.
 11. The intervertebral spacer device of claim 10,wherein the access hole is surrounded by a circular recess, and the capis secured in the circular recess.
 12. The intervertebral spacer deviceof claim 10, wherein the cap is compression locked to the secondbaseplate.
 13. The intervertebral spacer device of claim 10, wherein atleast one of the curvate pockets has a hemispherical contour.
 14. Theintervertebral spacer device of claim 9, wherein each of the inwardlyfacing surface of the first baseplate and the inwardly facing surface ofthe second baseplate has a respective perimeter region, and theperimeter regions have corresponding contours that reduce surfacewearing during rotation and angulation of the ball in the curvatesocket.
 15. The intervertebral spacer device of claim 9, wherein thecentral bore is tapered to a larger diameter toward the secondbaseplate's inwardly facing surface, and the post is accommodated, bythe central bore being tapered, for angulation in the central bore aboutthe ball's central portion as the ball angulates in the curvate socket.16. The intervertebral spacer device of claim 9, wherein the cap has anoutwardly facing surface and at least one of the first baseplate and thecap has an osteoinductive vertebral body contact surface on itsoutwardly facing surface.
 17. An artificial intervertebral disc,comprising: a first baseplate, having an outwardly facing surface and aninwardly facing surface, the inwardly facing surface having a centralhole; a second baseplate, having an outwardly facing surface and aninwardly facing surface; an inwardly directed convex structure integralwith the second baseplate, the convex structure forming a curvate pockethaving a semispherical contour on the second baseplate's outwardlyfacing surface, the convex structure further having a bore aligned withthe central hole and passing from the convex structure's curvate pocketto the second baseplate's inwardly facing surface; a ball at a head endof a post, the ball being seatable in the convex structure's curvatepocket with the post disposed through the bore, the post having a tailend securable in the central hole; and a cap forming a curvate pockethaving a semispherical contour, the cap being securable to the secondbaseplate with the cap's curvate pocket opposing the convex structure'scurvate pocket to form a curvate socket within which the ball isrotatable and angulatable about a central portion of the ball, the caphousing a spring member such that a compressive load applied to theoutwardly facing surfaces of the baseplates is borne by the springmember.
 18. The intervertebral spacer device of claim 17, wherein eachof the inwardly facing surface of the first baseplate and the inwardlyfacing surface of the second baseplate has a respective perimeterregion, and the perimeter regions have corresponding contours thatreduce surface wearing during rotation and angulation of the ball in thecurvate socket.
 19. The artificial intervertebral disc of claim 17,wherein each of the inwardly facing surface of the first baseplate andthe inwardly facing surface of the second baseplate has a respectiveperimeter region, and the ball's curvate recess's boundaries accommodateangulation of the ball within the curvate socket at least until theperimeter regions meet, and wherein the bore is tapered to a largerdiameter toward the inwardly facing surface of the second baseplate, andwherein the post is accommodated, by the bore being tapered, forangulation in the bore about the ball's central portion, as the ballangulates in the curvate socket, at least until the perimeter regionsmeet.
 20. The artificial intervertebral disc of claim 17, wherein thecap has an outwardly facing surface and at least one of the firstbaseplate and the cap has an osteoinductive vertebral body contactsurface on its outwardly facing surface.